diff --git a/book/10-begin/api/server/api/team-leader.ts b/book/10-begin/api/server/api/team-leader.ts
index db9eecc5..fabeb733 100644
--- a/book/10-begin/api/server/api/team-leader.ts
+++ b/book/10-begin/api/server/api/team-leader.ts
@@ -93,11 +93,11 @@ router.post('/stripe/fetch-checkout-session', async (req, res, next) => {
   try {
     const { mode, teamId } = req.body;
 
-    const user = await User.findById(req.user.id).select(['stripeCustomer', 'email']).lean();
+    const user = await User.findById(req.user.id).select(['stripeCustomer', 'email']).setOptions({ lean: true });
 
     const team = await Team.findById(teamId)
       .select(['stripeSubscription', 'slug', 'teamLeaderId'])
-      .lean();
+      .setOptions({ lean: true });
 
     if (!user || !team || team.teamLeaderId !== req.user.id) {
       throw new Error('Permission denied');
diff --git a/book/10-begin/api/server/aws-s3.ts b/book/10-begin/api/server/aws-s3.ts
index 6d50475b..bf432d48 100644
--- a/book/10-begin/api/server/aws-s3.ts
+++ b/book/10-begin/api/server/aws-s3.ts
@@ -21,7 +21,7 @@ async function signRequestForUpload({ fileName, fileType, prefix, bucket }) {
 
   const s3 = new aws.S3({
     apiVersion: 'latest',
-    region: 'us-east-1',
+    region: process.env.AWS_REGION,
     accessKeyId: process.env.AWS_ACCESSKEYID,
     secretAccessKey: process.env.AWS_SECRETACCESSKEY,
   });
diff --git a/book/10-begin/api/server/aws-ses.ts b/book/10-begin/api/server/aws-ses.ts
index faf399eb..fff1565e 100644
--- a/book/10-begin/api/server/aws-ses.ts
+++ b/book/10-begin/api/server/aws-ses.ts
@@ -3,7 +3,7 @@ import * as aws from 'aws-sdk';
 export default function sendEmail(options) {
   const ses = new aws.SES({
     apiVersion: 'latest',
-    region: 'us-east-1',
+    region: process.env.AWS_REGION,
     accessKeyId: process.env.AWS_ACCESSKEYID,
     secretAccessKey: process.env.AWS_SECRETACCESSKEY,
   });
diff --git a/book/10-begin/api/server/models/Discussion.ts b/book/10-begin/api/server/models/Discussion.ts
index e9931e9d..a5d8869f 100644
--- a/book/10-begin/api/server/models/Discussion.ts
+++ b/book/10-begin/api/server/models/Discussion.ts
@@ -24,7 +24,11 @@ const mongoSchema = new mongoose.Schema({
     type: String,
     required: true,
   },
-  memberIds: [String],
+  memberIds: [
+    {
+      type: String,
+    },
+  ],
   createdAt: {
     type: Date,
     required: true,
@@ -104,7 +108,7 @@ class DiscussionClass extends mongoose.Model {
 
     const filter: any = { teamId, memberIds: userId };
 
-    const discussions: any[] = await this.find(filter).lean();
+    const discussions: any[] = await this.find(filter).setOptions({ lean: true });
 
     return { discussions };
   }
@@ -134,7 +138,7 @@ class DiscussionClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const discussion = await this.findById(id).select('teamId createdUserId').lean();
+    const discussion = await this.findById(id).select('teamId createdUserId').setOptions({ lean: true });
 
     const team = await this.checkPermissionAndGetTeam({
       userId,
@@ -164,7 +168,7 @@ class DiscussionClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const discussion = await this.findById(id).select('teamId').lean();
+    const discussion = await this.findById(id).select('teamId').setOptions({ lean: true });
 
     await this.checkPermissionAndGetTeam({ userId, teamId: discussion.teamId });
 
@@ -180,7 +184,7 @@ class DiscussionClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const team = await Team.findById(teamId).select('memberIds teamLeaderId').lean();
+    const team = await Team.findById(teamId).select('memberIds teamLeaderId').setOptions({ lean: true });
 
     if (!team || team.memberIds.indexOf(userId) === -1) {
       throw new Error('Team not found');
diff --git a/book/10-begin/api/server/models/EmailTemplate.ts b/book/10-begin/api/server/models/EmailTemplate.ts
index 54ca2241..db9089d7 100644
--- a/book/10-begin/api/server/models/EmailTemplate.ts
+++ b/book/10-begin/api/server/models/EmailTemplate.ts
@@ -74,7 +74,7 @@ export async function insertTemplates() {
   ];
 
   for (const t of templates) {
-    const et = await EmailTemplate.findOne({ name: t.name }).lean();
+    const et = await EmailTemplate.findOne({ name: t.name }).setOptions({ lean: true });
     const message = t.message.replace(/\n/g, '').replace(/[ ]+/g, ' ').trim();
 
     if (!et) {
@@ -88,7 +88,7 @@ export async function insertTemplates() {
 export default async function getEmailTemplate(name: string, params: any) {
   await insertTemplates();
 
-  const et = await EmailTemplate.findOne({ name }).lean();
+  const et = await EmailTemplate.findOne({ name }).setOptions({ lean: true });
 
   if (!et) {
     throw new Error('Email Template is not found in database.');
diff --git a/book/10-begin/api/server/models/Invitation.ts b/book/10-begin/api/server/models/Invitation.ts
index c1d15471..60cd8dcf 100644
--- a/book/10-begin/api/server/models/Invitation.ts
+++ b/book/10-begin/api/server/models/Invitation.ts
@@ -68,12 +68,12 @@ class InvitationClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const team = await Team.findById(teamId).lean();
+    const team = await Team.findById(teamId).setOptions({ lean: true });
     if (!team || team.teamLeaderId !== userId) {
       throw new Error('Team does not exist or you have no permission');
     }
 
-    const registeredUser = await User.findOne({ email }).select('defaultTeamSlug').lean();
+    const registeredUser = await User.findOne({ email }).select('defaultTeamSlug').setOptions({ lean: true });
 
     if (registeredUser) {
       if (team.memberIds.includes(registeredUser._id.toString())) {
@@ -90,7 +90,7 @@ class InvitationClass extends mongoose.Model {
     }
 
     let token;
-    const invitation = await this.findOne({ teamId, email }).select('token').lean();
+    const invitation = await this.findOne({ teamId, email }).select('token').setOptions({ lean: true });
 
     if (invitation) {
       token = invitation.token;
@@ -125,17 +125,17 @@ class InvitationClass extends mongoose.Model {
       console.log('Email sending error:', err);
     });
 
-    return await this.findOne({ teamId, email }).lean();
+    return await this.findOne({ teamId, email }).setOptions({ lean: true });
   }
 
   public static async getTeamInvitations({ userId, teamId }) {
-    const team = await Team.findOne({ _id: teamId }).select('teamLeaderId').lean();
+    const team = await Team.findOne({ _id: teamId }).select('teamLeaderId').setOptions({ lean: true });
 
     if (userId !== team.teamLeaderId) {
       throw new Error('You have no permission.');
     }
 
-    return this.find({ teamId }).select('email').lean();
+    return this.find({ teamId }).select('email').setOptions({ lean: true });
   }
 
   public static async getTeamByToken({ token }) {
@@ -143,7 +143,7 @@ class InvitationClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const invitation = await this.findOne({ token }).lean();
+    const invitation = await this.findOne({ token }).setOptions({ lean: true });
 
     if (!invitation) {
       throw new Error('Invitation not found');
@@ -151,7 +151,7 @@ class InvitationClass extends mongoose.Model {
 
     const team = await Team.findById(invitation.teamId)
       .select('name slug avatarUrl memberIds')
-      .lean();
+      .setOptions({ lean: true });
 
     if (!team) {
       throw new Error('Team does not exist');
@@ -165,7 +165,7 @@ class InvitationClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const invitation = await this.findOne({ token }).lean();
+    const invitation = await this.findOne({ token }).setOptions({ lean: true });
 
     if (!invitation) {
       throw new Error('Invitation not found');
@@ -173,7 +173,7 @@ class InvitationClass extends mongoose.Model {
 
     const team = await Team.findById(invitation.teamId)
       .select('name slug avatarUrl memberIds')
-      .lean();
+      .setOptions({ lean: true });
 
     if (!team) {
       throw new Error('Team does not exist');
@@ -189,7 +189,7 @@ class InvitationClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const invitation = await this.findOne({ token }).lean();
+    const invitation = await this.findOne({ token }).setOptions({ lean: true });
 
     if (!invitation || invitation.email !== user.email) {
       throw new Error('Invitation not found');
@@ -199,7 +199,7 @@ class InvitationClass extends mongoose.Model {
 
     const team = await Team.findById(invitation.teamId)
       .select('memberIds slug teamLeaderId')
-      .lean();
+      .setOptions({ lean: true });
 
     if (!team) {
       throw new Error('Team does not exist');
diff --git a/book/10-begin/api/server/models/Post.ts b/book/10-begin/api/server/models/Post.ts
index ec47eab1..44e695e4 100644
--- a/book/10-begin/api/server/models/Post.ts
+++ b/book/10-begin/api/server/models/Post.ts
@@ -126,7 +126,7 @@ class PostClass extends mongoose.Model {
 
     const filter: any = { discussionId };
 
-    const posts: any[] = await this.find(filter).sort({ createdAt: 1 }).lean();
+    const posts: any[] = await this.find(filter).sort({ createdAt: 1 }).setOptions({ lean: true });
 
     return posts;
   }
@@ -156,7 +156,7 @@ class PostClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const post = await this.findById(id).select('createdUserId discussionId').lean();
+    const post = await this.findById(id).select('createdUserId discussionId').setOptions({ lean: true });
 
     await this.checkPermissionAndGetTeamAndDiscussion({
       userId,
@@ -180,7 +180,7 @@ class PostClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const post = await this.findById(id).select('createdUserId discussionId content').lean();
+    const post = await this.findById(id).select('createdUserId discussionId content').setOptions({ lean: true });
 
     await this.checkPermissionAndGetTeamAndDiscussion({
       userId,
@@ -206,7 +206,7 @@ class PostClass extends mongoose.Model {
 
     const discussion = await Discussion.findById(discussionId)
       .select('teamId memberIds slug')
-      .lean();
+      .setOptions({ lean: true });
 
     if (!discussion) {
       throw new Error('Discussion not found');
@@ -216,7 +216,7 @@ class PostClass extends mongoose.Model {
       throw new Error('Permission denied');
     }
 
-    const team = await Team.findById(discussion.teamId).select('memberIds slug').lean();
+    const team = await Team.findById(discussion.teamId).select('memberIds slug').setOptions({ lean: true });
 
     if (!team || team.memberIds.indexOf(userId) === -1) {
       throw new Error('Team not found');
diff --git a/book/10-begin/api/server/models/Team.ts b/book/10-begin/api/server/models/Team.ts
index 49a2eb2f..047cc105 100644
--- a/book/10-begin/api/server/models/Team.ts
+++ b/book/10-begin/api/server/models/Team.ts
@@ -26,10 +26,12 @@ const mongoSchema = new mongoose.Schema({
     type: String,
     required: true,
   },
-  memberIds: {
-    type: [String],
-    required: true,
-  },
+  memberIds: [
+    {
+      type: String,
+      required: true,
+    },
+  ],
   defaultTeam: {
     type: Boolean,
     default: false,
@@ -183,12 +185,12 @@ class TeamClass extends mongoose.Model {
 
     await this.updateOne({ _id: teamId }, { $set: modifier }, { runValidators: true });
 
-    return this.findById(teamId, 'name avatarUrl slug defaultTeam').lean();
+    return this.findById(teamId, 'name avatarUrl slug defaultTeam').setOptions({ lean: true });
   }
 
   public static getAllTeamsForUser(userId: string) {
     console.log(`userId:${userId}`);
-    return this.find({ memberIds: userId }).lean();
+    return this.find({ memberIds: userId }).setOptions({ lean: true });
   }
 
   public static async removeMember({ teamId, teamLeaderId, userId }) {
@@ -259,13 +261,13 @@ class TeamClass extends mongoose.Model {
       { new: true, runValidators: true },
     )
       .select('isSubscriptionActive stripeSubscription')
-      .lean();
+      .setOptions({ lean: true });
   }
 
   public static async cancelSubscriptionAfterFailedPayment({ subscriptionId }) {
     const team: any = await this.find({ 'stripeSubscription.id': subscriptionId })
       .select('teamLeaderId isSubscriptionActive stripeSubscription isPaymentFailed')
-      .lean();
+      .setOptions({ lean: true });
     if (!team.isSubscriptionActive) {
       throw new Error('Team is already unsubscribed.');
     }
@@ -285,7 +287,7 @@ class TeamClass extends mongoose.Model {
       { new: true, runValidators: true },
     )
       .select('isSubscriptionActive stripeSubscription isPaymentFailed')
-      .lean();
+      .setOptions({ lean: true });
   }
 }
 
diff --git a/book/10-begin/api/server/models/User.ts b/book/10-begin/api/server/models/User.ts
index 9dd1158d..639487fa 100644
--- a/book/10-begin/api/server/models/User.ts
+++ b/book/10-begin/api/server/models/User.ts
@@ -221,7 +221,7 @@ class UserClass extends mongoose.Model {
   public static async getUserBySlug({ slug }) {
     console.log('Static method: getUserBySlug');
 
-    return this.findOne({ slug }, 'email displayName avatarUrl').lean();
+    return this.findOne({ slug }, 'email displayName avatarUrl').setOptions({ lean: true });
   }
 
   public static async updateProfile({ userId, name, avatarUrl }) {
@@ -240,7 +240,7 @@ class UserClass extends mongoose.Model {
 
     return this.findByIdAndUpdate(userId, { $set: modifier }, { new: true, runValidators: true })
       .select('displayName avatarUrl slug')
-      .lean();
+      .setOptions({ lean: true });
   }
 
   public static publicFields(): string[] {
@@ -269,7 +269,7 @@ class UserClass extends mongoose.Model {
   }) {
     const user = await this.findOne({ email })
       .select([...this.publicFields(), 'googleId'].join(' '))
-      .lean();
+      .setOptions({ lean: true });
 
     if (user) {
       if (_.isEmpty(googleToken) && user.googleId) {
@@ -331,7 +331,7 @@ class UserClass extends mongoose.Model {
   }
 
   public static async signInOrSignUpByPasswordless({ uid, email }) {
-    const user = await this.findOne({ email }).select(this.publicFields().join(' ')).lean();
+    const user = await this.findOne({ email }).select(this.publicFields().join(' ')).setOptions({ lean: true });
 
     if (user) {
       throw Error('User already exists');
@@ -382,7 +382,7 @@ class UserClass extends mongoose.Model {
 
     return this.find({ _id: { $in: team.memberIds } })
       .select(this.publicFields().join(' '))
-      .lean();
+      .setOptions({ lean: true });
   }
 
   public static async saveStripeCustomerAndCard({
@@ -456,7 +456,7 @@ class UserClass extends mongoose.Model {
 
     return this.findByIdAndUpdate(userId, { $set: modifier }, { new: true, runValidators: true })
       .select('stripeListOfInvoices')
-      .lean();
+      .setOptions({ lean: true });
   }
 
   private static async checkPermissionAndGetTeam({ userId, teamId }) {
@@ -466,7 +466,7 @@ class UserClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const team = await Team.findById(teamId).select('memberIds').lean();
+    const team = await Team.findById(teamId).select('memberIds').setOptions({ lean: true });
 
     if (!team || team.memberIds.indexOf(userId) === -1) {
       throw new Error('Team not found');
diff --git a/book/10-begin/api/server/passwordless-auth.ts b/book/10-begin/api/server/passwordless-auth.ts
index 3b3292b4..ac354223 100644
--- a/book/10-begin/api/server/passwordless-auth.ts
+++ b/book/10-begin/api/server/passwordless-auth.ts
@@ -50,7 +50,7 @@ function setupPasswordless({ server }) {
     '/auth/email-login-link',
     passwordless.requestToken(async (email, __, callback) => {
       try {
-        const user = await User.findOne({ email }).select('_id').lean();
+        const user = await User.findOne({ email }).select('_id').setOptions({ lean: true });
 
         if (user) {
           callback(null, user._id);
diff --git a/book/10-begin/api/server/passwordless-token-mongostore.ts b/book/10-begin/api/server/passwordless-token-mongostore.ts
index 7cd4825c..25eef0b5 100644
--- a/book/10-begin/api/server/passwordless-token-mongostore.ts
+++ b/book/10-begin/api/server/passwordless-token-mongostore.ts
@@ -52,7 +52,7 @@ MongoStore.prototype.authenticate = async function (token, uid, callback) {
   }
 
   try {
-    const tokenDoc = await PasswordlessToken.findOne({ uid, ttl: { $gt: new Date() } }).lean();
+    const tokenDoc = await PasswordlessToken.findOne({ uid, ttl: { $gt: new Date() } }).setOptions({ lean: true });
 
     if (tokenDoc) {
       const isMatch = await bcrypt.compare(token, tokenDoc.hashedToken);
@@ -130,7 +130,7 @@ MongoStore.prototype.storeOrUpdateByEmail = async function addEmail(email: strin
     throw new Error('TokenStore:addEmail called with invalid parameters');
   }
 
-  const obj = await PasswordlessToken.findOne({ email }).select('uid').lean();
+  const obj = await PasswordlessToken.findOne({ email }).select('uid').setOptions({ lean: true });
 
   if (obj) {
     return obj.uid;
diff --git a/book/10-begin/api/server/stripe.ts b/book/10-begin/api/server/stripe.ts
index a0f0b116..90d7080d 100644
--- a/book/10-begin/api/server/stripe.ts
+++ b/book/10-begin/api/server/stripe.ts
@@ -121,12 +121,12 @@ function stripeWebhookAndCheckoutCallback({ server }) {
     const user = await User.findById(
       session.metadata.userId,
       '_id stripeCustomer email displayName isSubscriptionActive stripeSubscription',
-    ).lean();
+    ).setOptions({ lean: true });
 
     const team = await Team.findById(
       session.metadata.teamId,
       'isSubscriptionActive stripeSubscription teamLeaderId slug',
-    ).lean();
+    ).setOptions({ lean: true });
 
     if (!user) {
       throw new Error('User not found.');
diff --git a/book/10-begin/api/server/utils/slugify.ts b/book/10-begin/api/server/utils/slugify.ts
index e76af3c6..f2394edd 100644
--- a/book/10-begin/api/server/utils/slugify.ts
+++ b/book/10-begin/api/server/utils/slugify.ts
@@ -5,7 +5,7 @@ const slugify = (text) => _.kebabCase(text);
 async function createUniqueSlug(Model, slug, count, filter) {
   const obj = await Model.findOne({ slug: `${slug}-${count}`, ...filter })
     .select('_id')
-    .lean();
+    .setOptions({ lean: true });
 
   if (!obj) {
     return `${slug}-${count}`;
@@ -19,7 +19,7 @@ async function generateSlug(Model, name, filter = {}) {
 
   const obj = await Model.findOne({ slug: origSlug, ...filter })
     .select('_id')
-    .lean();
+    .setOptions({ lean: true });
 
   if (!obj) {
     return origSlug;
@@ -31,7 +31,7 @@ async function generateSlug(Model, name, filter = {}) {
 async function generateNumberSlug(Model, filter = {}, n = 1) {
   const obj = await Model.findOne({ slug: n, ...filter })
     .select('_id')
-    .lean();
+    .setOptions({ lean: true });
 
   if (!obj) {
     return `${n}`;
diff --git a/book/10-begin/lambda/handler.ts b/book/10-begin/lambda/handler.ts
index 43918a6c..26fa72d2 100644
--- a/book/10-begin/lambda/handler.ts
+++ b/book/10-begin/lambda/handler.ts
@@ -39,7 +39,7 @@ export const sendEmailForNewPost = async (event) => {
 
     const usersToNotify = await User.find({ _id: { $in: userIds } })
       .select('email')
-      .lean();
+      .setOptions({ lean: true });
 
     console.log('usersToNotify', usersToNotify);
 
diff --git a/book/10-end/api/server/api/team-leader.ts b/book/10-end/api/server/api/team-leader.ts
index db9eecc5..fabeb733 100644
--- a/book/10-end/api/server/api/team-leader.ts
+++ b/book/10-end/api/server/api/team-leader.ts
@@ -93,11 +93,11 @@ router.post('/stripe/fetch-checkout-session', async (req, res, next) => {
   try {
     const { mode, teamId } = req.body;
 
-    const user = await User.findById(req.user.id).select(['stripeCustomer', 'email']).lean();
+    const user = await User.findById(req.user.id).select(['stripeCustomer', 'email']).setOptions({ lean: true });
 
     const team = await Team.findById(teamId)
       .select(['stripeSubscription', 'slug', 'teamLeaderId'])
-      .lean();
+      .setOptions({ lean: true });
 
     if (!user || !team || team.teamLeaderId !== req.user.id) {
       throw new Error('Permission denied');
diff --git a/book/10-end/api/server/aws-s3.ts b/book/10-end/api/server/aws-s3.ts
index 6d50475b..28d938b7 100644
--- a/book/10-end/api/server/aws-s3.ts
+++ b/book/10-end/api/server/aws-s3.ts
@@ -1,7 +1,17 @@
 import * as url from 'url';
 import * as aws from 'aws-sdk';
 
-async function signRequestForUpload({ fileName, fileType, prefix, bucket }) {
+async function signRequestForUpload({
+  fileName,
+  fileType,
+  prefix,
+  bucket,
+}: {
+  fileName: string;
+  fileType: string;
+  prefix: string;
+  bucket: string;
+}) {
   const randomStringForPrefix =
     Math.random().toString(36).substring(2, 12) + Math.random().toString(36).substring(2, 12);
 
@@ -21,7 +31,7 @@ async function signRequestForUpload({ fileName, fileType, prefix, bucket }) {
 
   const s3 = new aws.S3({
     apiVersion: 'latest',
-    region: 'us-east-1',
+    region: process.env.AWS_REGION,
     accessKeyId: process.env.AWS_ACCESSKEYID,
     secretAccessKey: process.env.AWS_SECRETACCESSKEY,
   });
diff --git a/book/10-end/api/server/aws-ses.ts b/book/10-end/api/server/aws-ses.ts
index faf399eb..fff1565e 100644
--- a/book/10-end/api/server/aws-ses.ts
+++ b/book/10-end/api/server/aws-ses.ts
@@ -3,7 +3,7 @@ import * as aws from 'aws-sdk';
 export default function sendEmail(options) {
   const ses = new aws.SES({
     apiVersion: 'latest',
-    region: 'us-east-1',
+    region: process.env.AWS_REGION,
     accessKeyId: process.env.AWS_ACCESSKEYID,
     secretAccessKey: process.env.AWS_SECRETACCESSKEY,
   });
diff --git a/book/10-end/api/server/mailchimp.ts b/book/10-end/api/server/mailchimp.ts
index 6f3eb9ef..7abf8d5e 100644
--- a/book/10-end/api/server/mailchimp.ts
+++ b/book/10-end/api/server/mailchimp.ts
@@ -4,7 +4,18 @@ const LIST_IDS = {
   signups: process.env.MAILCHIMP_SAAS_ALL_LIST_ID,
 };
 
-function callAPI({ path, method, data }): Promise<Response> {
+function callAPI({
+  path,
+  method,
+  data,
+}: {
+  path: string;
+  method: string;
+  data: {
+    email_address: string;
+    status: string;
+  };
+}): Promise<Response> {
   const ROOT_URI = `https://${process.env.MAILCHIMP_REGION}.api.mailchimp.com/3.0`;
 
   return fetch(`${ROOT_URI}${path}`, {
@@ -19,9 +30,8 @@ function callAPI({ path, method, data }): Promise<Response> {
   });
 }
 
-async function addToMailchimp({ email, listName }) {
+async function addToMailchimp({ email, listName }: { email: string; listName: string }) {
   const data = {
-    // eslint-disable-next-line
     email_address: email,
     status: 'subscribed',
   };
diff --git a/book/10-end/api/server/models/Discussion.ts b/book/10-end/api/server/models/Discussion.ts
index e9931e9d..a5d8869f 100644
--- a/book/10-end/api/server/models/Discussion.ts
+++ b/book/10-end/api/server/models/Discussion.ts
@@ -24,7 +24,11 @@ const mongoSchema = new mongoose.Schema({
     type: String,
     required: true,
   },
-  memberIds: [String],
+  memberIds: [
+    {
+      type: String,
+    },
+  ],
   createdAt: {
     type: Date,
     required: true,
@@ -104,7 +108,7 @@ class DiscussionClass extends mongoose.Model {
 
     const filter: any = { teamId, memberIds: userId };
 
-    const discussions: any[] = await this.find(filter).lean();
+    const discussions: any[] = await this.find(filter).setOptions({ lean: true });
 
     return { discussions };
   }
@@ -134,7 +138,7 @@ class DiscussionClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const discussion = await this.findById(id).select('teamId createdUserId').lean();
+    const discussion = await this.findById(id).select('teamId createdUserId').setOptions({ lean: true });
 
     const team = await this.checkPermissionAndGetTeam({
       userId,
@@ -164,7 +168,7 @@ class DiscussionClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const discussion = await this.findById(id).select('teamId').lean();
+    const discussion = await this.findById(id).select('teamId').setOptions({ lean: true });
 
     await this.checkPermissionAndGetTeam({ userId, teamId: discussion.teamId });
 
@@ -180,7 +184,7 @@ class DiscussionClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const team = await Team.findById(teamId).select('memberIds teamLeaderId').lean();
+    const team = await Team.findById(teamId).select('memberIds teamLeaderId').setOptions({ lean: true });
 
     if (!team || team.memberIds.indexOf(userId) === -1) {
       throw new Error('Team not found');
diff --git a/book/10-end/api/server/models/EmailTemplate.ts b/book/10-end/api/server/models/EmailTemplate.ts
index 54ca2241..db9089d7 100644
--- a/book/10-end/api/server/models/EmailTemplate.ts
+++ b/book/10-end/api/server/models/EmailTemplate.ts
@@ -74,7 +74,7 @@ export async function insertTemplates() {
   ];
 
   for (const t of templates) {
-    const et = await EmailTemplate.findOne({ name: t.name }).lean();
+    const et = await EmailTemplate.findOne({ name: t.name }).setOptions({ lean: true });
     const message = t.message.replace(/\n/g, '').replace(/[ ]+/g, ' ').trim();
 
     if (!et) {
@@ -88,7 +88,7 @@ export async function insertTemplates() {
 export default async function getEmailTemplate(name: string, params: any) {
   await insertTemplates();
 
-  const et = await EmailTemplate.findOne({ name }).lean();
+  const et = await EmailTemplate.findOne({ name }).setOptions({ lean: true });
 
   if (!et) {
     throw new Error('Email Template is not found in database.');
diff --git a/book/10-end/api/server/models/Invitation.ts b/book/10-end/api/server/models/Invitation.ts
index f36745d8..2a46dd49 100644
--- a/book/10-end/api/server/models/Invitation.ts
+++ b/book/10-end/api/server/models/Invitation.ts
@@ -68,12 +68,14 @@ class InvitationClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const team = await Team.findById(teamId).lean();
+    const team = await Team.findById(teamId).setOptions({ lean: true });
     if (!team || team.teamLeaderId !== userId) {
       throw new Error('Team does not exist or you have no permission');
     }
 
-    const registeredUser = await User.findOne({ email }).select('defaultTeamSlug').lean();
+    const registeredUser = await User.findOne({ email })
+      .select('defaultTeamSlug')
+      .setOptions({ lean: true });
 
     if (registeredUser) {
       if (team.memberIds.includes(registeredUser._id.toString())) {
@@ -90,7 +92,9 @@ class InvitationClass extends mongoose.Model {
     }
 
     let token;
-    const invitation = await this.findOne({ teamId, email }).select('token').lean();
+    const invitation = await this.findOne({ teamId, email })
+      .select('token')
+      .setOptions({ lean: true });
 
     if (invitation) {
       token = invitation.token;
@@ -129,17 +133,19 @@ class InvitationClass extends mongoose.Model {
       console.log('Email sending error:', err);
     });
 
-    return await this.findOne({ teamId, email }).lean();
+    return await this.findOne({ teamId, email }).setOptions({ lean: true });
   }
 
   public static async getTeamInvitations({ userId, teamId }) {
-    const team = await Team.findOne({ _id: teamId }).select('teamLeaderId').lean();
+    const team = await Team.findOne({ _id: teamId })
+      .select('teamLeaderId')
+      .setOptions({ lean: true });
 
     if (userId !== team.teamLeaderId) {
       throw new Error('You have no permission.');
     }
 
-    return this.find({ teamId }).select('email').lean();
+    return this.find({ teamId }).select('email').setOptions({ lean: true });
   }
 
   public static async getTeamByToken({ token }) {
@@ -147,7 +153,7 @@ class InvitationClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const invitation = await this.findOne({ token }).lean();
+    const invitation = await this.findOne({ token }).setOptions({ lean: true });
 
     if (!invitation) {
       throw new Error('Invitation not found');
@@ -155,7 +161,7 @@ class InvitationClass extends mongoose.Model {
 
     const team = await Team.findById(invitation.teamId)
       .select('name slug avatarUrl memberIds')
-      .lean();
+      .setOptions({ lean: true });
 
     if (!team) {
       throw new Error('Team does not exist');
@@ -169,7 +175,7 @@ class InvitationClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const invitation = await this.findOne({ token }).lean();
+    const invitation = await this.findOne({ token }).setOptions({ lean: true });
 
     if (!invitation) {
       throw new Error('Invitation not found');
@@ -177,7 +183,7 @@ class InvitationClass extends mongoose.Model {
 
     const team = await Team.findById(invitation.teamId)
       .select('name slug avatarUrl memberIds')
-      .lean();
+      .setOptions({ lean: true });
 
     if (!team) {
       throw new Error('Team does not exist');
@@ -193,7 +199,7 @@ class InvitationClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const invitation = await this.findOne({ token }).lean();
+    const invitation = await this.findOne({ token }).setOptions({ lean: true });
 
     if (!invitation || invitation.email !== user.email) {
       throw new Error('Invitation not found');
@@ -203,7 +209,7 @@ class InvitationClass extends mongoose.Model {
 
     const team = await Team.findById(invitation.teamId)
       .select('memberIds slug teamLeaderId')
-      .lean();
+      .setOptions({ lean: true });
 
     if (!team) {
       throw new Error('Team does not exist');
diff --git a/book/10-end/api/server/models/Post.ts b/book/10-end/api/server/models/Post.ts
index ec47eab1..44e695e4 100644
--- a/book/10-end/api/server/models/Post.ts
+++ b/book/10-end/api/server/models/Post.ts
@@ -126,7 +126,7 @@ class PostClass extends mongoose.Model {
 
     const filter: any = { discussionId };
 
-    const posts: any[] = await this.find(filter).sort({ createdAt: 1 }).lean();
+    const posts: any[] = await this.find(filter).sort({ createdAt: 1 }).setOptions({ lean: true });
 
     return posts;
   }
@@ -156,7 +156,7 @@ class PostClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const post = await this.findById(id).select('createdUserId discussionId').lean();
+    const post = await this.findById(id).select('createdUserId discussionId').setOptions({ lean: true });
 
     await this.checkPermissionAndGetTeamAndDiscussion({
       userId,
@@ -180,7 +180,7 @@ class PostClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const post = await this.findById(id).select('createdUserId discussionId content').lean();
+    const post = await this.findById(id).select('createdUserId discussionId content').setOptions({ lean: true });
 
     await this.checkPermissionAndGetTeamAndDiscussion({
       userId,
@@ -206,7 +206,7 @@ class PostClass extends mongoose.Model {
 
     const discussion = await Discussion.findById(discussionId)
       .select('teamId memberIds slug')
-      .lean();
+      .setOptions({ lean: true });
 
     if (!discussion) {
       throw new Error('Discussion not found');
@@ -216,7 +216,7 @@ class PostClass extends mongoose.Model {
       throw new Error('Permission denied');
     }
 
-    const team = await Team.findById(discussion.teamId).select('memberIds slug').lean();
+    const team = await Team.findById(discussion.teamId).select('memberIds slug').setOptions({ lean: true });
 
     if (!team || team.memberIds.indexOf(userId) === -1) {
       throw new Error('Team not found');
diff --git a/book/10-end/api/server/models/Team.ts b/book/10-end/api/server/models/Team.ts
index 49a2eb2f..047cc105 100644
--- a/book/10-end/api/server/models/Team.ts
+++ b/book/10-end/api/server/models/Team.ts
@@ -26,10 +26,12 @@ const mongoSchema = new mongoose.Schema({
     type: String,
     required: true,
   },
-  memberIds: {
-    type: [String],
-    required: true,
-  },
+  memberIds: [
+    {
+      type: String,
+      required: true,
+    },
+  ],
   defaultTeam: {
     type: Boolean,
     default: false,
@@ -183,12 +185,12 @@ class TeamClass extends mongoose.Model {
 
     await this.updateOne({ _id: teamId }, { $set: modifier }, { runValidators: true });
 
-    return this.findById(teamId, 'name avatarUrl slug defaultTeam').lean();
+    return this.findById(teamId, 'name avatarUrl slug defaultTeam').setOptions({ lean: true });
   }
 
   public static getAllTeamsForUser(userId: string) {
     console.log(`userId:${userId}`);
-    return this.find({ memberIds: userId }).lean();
+    return this.find({ memberIds: userId }).setOptions({ lean: true });
   }
 
   public static async removeMember({ teamId, teamLeaderId, userId }) {
@@ -259,13 +261,13 @@ class TeamClass extends mongoose.Model {
       { new: true, runValidators: true },
     )
       .select('isSubscriptionActive stripeSubscription')
-      .lean();
+      .setOptions({ lean: true });
   }
 
   public static async cancelSubscriptionAfterFailedPayment({ subscriptionId }) {
     const team: any = await this.find({ 'stripeSubscription.id': subscriptionId })
       .select('teamLeaderId isSubscriptionActive stripeSubscription isPaymentFailed')
-      .lean();
+      .setOptions({ lean: true });
     if (!team.isSubscriptionActive) {
       throw new Error('Team is already unsubscribed.');
     }
@@ -285,7 +287,7 @@ class TeamClass extends mongoose.Model {
       { new: true, runValidators: true },
     )
       .select('isSubscriptionActive stripeSubscription isPaymentFailed')
-      .lean();
+      .setOptions({ lean: true });
   }
 }
 
diff --git a/book/10-end/api/server/models/User.ts b/book/10-end/api/server/models/User.ts
index 972aa8d6..61129f7e 100644
--- a/book/10-end/api/server/models/User.ts
+++ b/book/10-end/api/server/models/User.ts
@@ -240,7 +240,7 @@ class UserClass extends mongoose.Model {
 
     return this.findByIdAndUpdate(userId, { $set: modifier }, { new: true, runValidators: true })
       .select('displayName avatarUrl slug')
-      .lean();
+      .setOptions({ lean: true });
   }
 
   public static publicFields(): string[] {
@@ -269,7 +269,7 @@ class UserClass extends mongoose.Model {
   }) {
     const user = await this.findOne({ email })
       .select([...this.publicFields(), 'googleId'].join(' '))
-      .lean();
+      .setOptions({ lean: true });
 
     if (user) {
       if (_.isEmpty(googleToken) && user.googleId) {
@@ -331,7 +331,7 @@ class UserClass extends mongoose.Model {
   }
 
   public static async signInOrSignUpByPasswordless({ uid, email }) {
-    const user = await this.findOne({ email }).select(this.publicFields().join(' ')).lean();
+    const user = await this.findOne({ email }).select(this.publicFields().join(' ')).setOptions({ lean: true });
 
     if (user) {
       throw Error('User already exists');
@@ -373,6 +373,7 @@ class UserClass extends mongoose.Model {
     return _.pick(newUser, this.publicFields());
   }
 
+  // try private instead of public, run `yarn build`
   public static toggleTheme({ userId, darkTheme }) {
     return this.updateOne({ _id: userId }, { darkTheme: !!darkTheme });
   }
@@ -382,7 +383,7 @@ class UserClass extends mongoose.Model {
 
     return this.find({ _id: { $in: team.memberIds } })
       .select(this.publicFields().join(' '))
-      .lean();
+      .setOptions({ lean: true });
   }
 
   public static async saveStripeCustomerAndCard({
@@ -456,7 +457,7 @@ class UserClass extends mongoose.Model {
 
     return this.findByIdAndUpdate(userId, { $set: modifier }, { new: true, runValidators: true })
       .select('stripeListOfInvoices')
-      .lean();
+      .setOptions({ lean: true });
   }
 
   private static async checkPermissionAndGetTeam({ userId, teamId }) {
@@ -466,7 +467,7 @@ class UserClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const team = await Team.findById(teamId).select('memberIds').lean();
+    const team = await Team.findById(teamId).select('memberIds').setOptions({ lean: true });
 
     if (!team || team.memberIds.indexOf(userId) === -1) {
       throw new Error('Team not found');
diff --git a/book/10-end/api/server/passwordless-auth.ts b/book/10-end/api/server/passwordless-auth.ts
index ba5b1986..db3748b9 100644
--- a/book/10-end/api/server/passwordless-auth.ts
+++ b/book/10-end/api/server/passwordless-auth.ts
@@ -52,7 +52,7 @@ function setupPasswordless({ server }) {
     '/auth/email-login-link',
     passwordless.requestToken(async (email, __, callback) => {
       try {
-        const user = await User.findOne({ email }).select('_id').lean();
+        const user = await User.findOne({ email }).select('_id').setOptions({ lean: true });
 
         if (user) {
           callback(null, user._id);
diff --git a/book/10-end/api/server/passwordless-token-mongostore.ts b/book/10-end/api/server/passwordless-token-mongostore.ts
index 7cd4825c..7ebc9c11 100644
--- a/book/10-end/api/server/passwordless-token-mongostore.ts
+++ b/book/10-end/api/server/passwordless-token-mongostore.ts
@@ -52,7 +52,9 @@ MongoStore.prototype.authenticate = async function (token, uid, callback) {
   }
 
   try {
-    const tokenDoc = await PasswordlessToken.findOne({ uid, ttl: { $gt: new Date() } }).lean();
+    const tokenDoc = await PasswordlessToken.findOne({ uid, ttl: { $gt: new Date() } }).setOptions({
+      lean: true,
+    });
 
     if (tokenDoc) {
       const isMatch = await bcrypt.compare(token, tokenDoc.hashedToken);
@@ -130,7 +132,7 @@ MongoStore.prototype.storeOrUpdateByEmail = async function addEmail(email: strin
     throw new Error('TokenStore:addEmail called with invalid parameters');
   }
 
-  const obj = await PasswordlessToken.findOne({ email }).select('uid').lean();
+  const obj = await PasswordlessToken.findOne({ email }).select('uid').setOptions({ lean: true });
 
   if (obj) {
     return obj.uid;
diff --git a/book/10-end/api/server/sockets.ts b/book/10-end/api/server/sockets.ts
index 5f1f3d46..50e21eee 100644
--- a/book/10-end/api/server/sockets.ts
+++ b/book/10-end/api/server/sockets.ts
@@ -1,5 +1,7 @@
 import { Response } from 'express';
+import * as express from 'express';
 import { Server } from 'socket.io';
+import * as httpModule from 'http';
 
 import { DiscussionDocument } from './models/Discussion';
 import { PostDocument } from './models/Post';
@@ -8,7 +10,15 @@ let io: Server = null;
 
 const dev = process.env.NODE_ENV !== 'production';
 
-function setupSockets({ httpServer, origin, sessionMiddleware }) {
+function setupSockets({
+  httpServer,
+  origin,
+  sessionMiddleware,
+}: {
+  httpServer: httpModule.Server;
+  origin: string | boolean | RegExp | (string | RegExp)[];
+  sessionMiddleware: express.RequestHandler;
+}) {
   if (io === null) {
     io = new Server(httpServer, {
       cors: {
@@ -19,7 +29,7 @@ function setupSockets({ httpServer, origin, sessionMiddleware }) {
       cookie: {
         httpOnly: true,
         maxAge: 14 * 24 * 60 * 60 * 1000, // expires in 14 days
-        domain: dev ? 'localhost' : '.builderbook.org', // update value in the next book update
+        domain: dev ? 'localhost' : '.async-await.com',
         secure: dev ? false : true,
       },
       serveClient: false,
diff --git a/book/10-end/api/server/stripe.ts b/book/10-end/api/server/stripe.ts
index ac3f2a96..87881e85 100644
--- a/book/10-end/api/server/stripe.ts
+++ b/book/10-end/api/server/stripe.ts
@@ -1,3 +1,4 @@
+import * as express from 'express';
 import * as bodyParser from 'body-parser';
 import Stripe from 'stripe';
 
@@ -13,7 +14,23 @@ const stripeInstance = new Stripe(
   { apiVersion: '2020-08-27' },
 );
 
-function createSession({ userId, teamId, teamSlug, customerId, subscriptionId, userEmail, mode }) {
+function createSession({
+  userId,
+  teamId,
+  teamSlug,
+  customerId,
+  subscriptionId,
+  userEmail,
+  mode,
+}: {
+  userId: string;
+  teamId: string;
+  teamSlug: string;
+  customerId: string;
+  subscriptionId: string;
+  userEmail: string;
+  mode: Stripe.Checkout.SessionCreateParams.Mode;
+}) {
   const params: Stripe.Checkout.SessionCreateParams = {
     customer_email: customerId ? undefined : userEmail,
     customer: customerId,
@@ -70,17 +87,17 @@ function updateSubscription(subscriptionId: string, params: Stripe.SubscriptionU
   return stripeInstance.subscriptions.update(subscriptionId, params);
 }
 
-function cancelSubscription({ subscriptionId }) {
+function cancelSubscription({ subscriptionId }: { subscriptionId: string }) {
   logger.debug('cancel subscription', subscriptionId);
   return stripeInstance.subscriptions.del(subscriptionId);
 }
 
-function getListOfInvoices({ customerId }) {
+function getListOfInvoices({ customerId }: { customerId: string }) {
   logger.debug('getting list of invoices for customer', customerId);
   return stripeInstance.invoices.list({ customer: customerId, limit: 100 });
 }
 
-function stripeWebhookAndCheckoutCallback({ server }) {
+function stripeWebhookAndCheckoutCallback({ server }: { server: express.Application }) {
   server.post(
     '/api/v1/public/stripe-invoice-payment-failed',
     bodyParser.raw({ type: 'application/json' }),
@@ -127,12 +144,12 @@ function stripeWebhookAndCheckoutCallback({ server }) {
     const user = await User.findById(
       session.metadata.userId,
       '_id stripeCustomer email displayName isSubscriptionActive stripeSubscription',
-    ).lean();
+    ).setOptions({ lean: true });
 
     const team = await Team.findById(
       session.metadata.teamId,
       'isSubscriptionActive stripeSubscription teamLeaderId slug',
-    ).lean();
+    ).setOptions({ lean: true });
 
     if (!user) {
       throw new Error('User not found.');
diff --git a/book/10-end/api/server/utils/slugify.ts b/book/10-end/api/server/utils/slugify.ts
index e76af3c6..f2394edd 100644
--- a/book/10-end/api/server/utils/slugify.ts
+++ b/book/10-end/api/server/utils/slugify.ts
@@ -5,7 +5,7 @@ const slugify = (text) => _.kebabCase(text);
 async function createUniqueSlug(Model, slug, count, filter) {
   const obj = await Model.findOne({ slug: `${slug}-${count}`, ...filter })
     .select('_id')
-    .lean();
+    .setOptions({ lean: true });
 
   if (!obj) {
     return `${slug}-${count}`;
@@ -19,7 +19,7 @@ async function generateSlug(Model, name, filter = {}) {
 
   const obj = await Model.findOne({ slug: origSlug, ...filter })
     .select('_id')
-    .lean();
+    .setOptions({ lean: true });
 
   if (!obj) {
     return origSlug;
@@ -31,7 +31,7 @@ async function generateSlug(Model, name, filter = {}) {
 async function generateNumberSlug(Model, filter = {}, n = 1) {
   const obj = await Model.findOne({ slug: n, ...filter })
     .select('_id')
-    .lean();
+    .setOptions({ lean: true });
 
   if (!obj) {
     return `${n}`;
diff --git a/book/10-end/app/server/server.ts b/book/10-end/app/server/server.ts
index 940c3874..2fc12b4c 100644
--- a/book/10-end/app/server/server.ts
+++ b/book/10-end/app/server/server.ts
@@ -81,6 +81,8 @@ app.prepare().then(() => {
     handle(req, res);
   });
 
+  // listen(handle: any, listeningListener?: () => void): http.Server;
+  // "@types/express-serve-static-core", "version": "4.17.1"
   server.listen(port, () => {
     console.log(`> Ready on ${dev ? process.env.URL_APP : process.env.PRODUCTION_URL_APP}`);
   });
diff --git a/book/10-end/lambda/handler.ts b/book/10-end/lambda/handler.ts
index a5e89456..ac907afb 100644
--- a/book/10-end/lambda/handler.ts
+++ b/book/10-end/lambda/handler.ts
@@ -46,7 +46,7 @@ export const sendEmailForNewPost = async (event) => {
 
     const usersToNotify = await User.find({ _id: { $in: userIds } })
       .select('email')
-      .lean();
+      .setOptions({ lean: true });
 
     console.log('usersToNotify', usersToNotify);
 
diff --git a/book/3-begin/app/server/server.ts b/book/3-begin/app/server/server.ts
index 01cfcf06..4d2bc446 100644
--- a/book/3-begin/app/server/server.ts
+++ b/book/3-begin/app/server/server.ts
@@ -26,10 +26,7 @@ app.prepare().then(() => {
     handle(req, res);
   });
 
-  server.listen(process.env.PORT_APP, (err) => {
-    if (err) {
-      throw err;
-    }
+  server.listen(process.env.PORT_APP, () => {
     console.log(`> Ready on ${process.env.URL_APP}`);
   });
 });
diff --git a/book/3-end/api/server/server.ts b/book/3-end/api/server/server.ts
index 875e55ca..8d74dee8 100644
--- a/book/3-end/api/server/server.ts
+++ b/book/3-end/api/server/server.ts
@@ -18,9 +18,6 @@ server.get('*', (_, res) => {
 
 console.log(process.env.PORT_API, process.env.URL_API);
 
-server.listen(process.env['PORT_API'], (err) => {
-  if (err) {
-    throw err;
-  }
+server.listen(process.env.PORT_API, () => {
   console.log(`> Ready on ${process.env.URL_API}`);
 });
diff --git a/book/3-end/app/server/server.ts b/book/3-end/app/server/server.ts
index 2ea549d6..095437fe 100644
--- a/book/3-end/app/server/server.ts
+++ b/book/3-end/app/server/server.ts
@@ -28,10 +28,7 @@ app.prepare().then(() => {
 
   console.log(process.env.PORT_APP);
 
-  server.listen(process.env.PORT_APP, (err) => {
-    if (err) {
-      throw err;
-    }
+  server.listen(process.env.PORT_APP, () => {
     console.log(`> Ready on ${process.env.URL_APP}`);
   });
 });
diff --git a/book/4-begin/api/server/server.ts b/book/4-begin/api/server/server.ts
index ad2e9e54..f6255b1d 100644
--- a/book/4-begin/api/server/server.ts
+++ b/book/4-begin/api/server/server.ts
@@ -16,9 +16,6 @@ server.get('*', (_, res) => {
   res.sendStatus(403);
 });
 
-server.listen(process.env.PORT_API, (err) => {
-  if (err) {
-    throw err;
-  }
+server.listen(process.env.PORT_API, () => {
   console.log(`> Ready on ${process.env.URL_API}`);
 });
diff --git a/book/4-begin/app/server/server.ts b/book/4-begin/app/server/server.ts
index 01cfcf06..4d2bc446 100644
--- a/book/4-begin/app/server/server.ts
+++ b/book/4-begin/app/server/server.ts
@@ -26,10 +26,7 @@ app.prepare().then(() => {
     handle(req, res);
   });
 
-  server.listen(process.env.PORT_APP, (err) => {
-    if (err) {
-      throw err;
-    }
+  server.listen(process.env.PORT_APP, () => {
     console.log(`> Ready on ${process.env.URL_APP}`);
   });
 });
diff --git a/book/4-end/api/server/aws-s3.ts b/book/4-end/api/server/aws-s3.ts
index 81b9671c..302b4659 100644
--- a/book/4-end/api/server/aws-s3.ts
+++ b/book/4-end/api/server/aws-s3.ts
@@ -21,7 +21,7 @@ async function signRequestForUpload({ fileName, fileType, prefix, bucket }) {
 
   const s3 = new aws.S3({
     apiVersion: 'latest',
-    region: 'us-east-1',
+    region: process.env.AWS_REGION,
     accessKeyId: process.env.AWS_ACCESSKEYID,
     secretAccessKey: process.env.AWS_SECRETACCESSKEY,
   });
diff --git a/book/4-end/api/server/models/User.ts b/book/4-end/api/server/models/User.ts
index 0077c773..45c07d22 100644
--- a/book/4-end/api/server/models/User.ts
+++ b/book/4-end/api/server/models/User.ts
@@ -50,7 +50,7 @@ class UserClass extends mongoose.Model {
   public static async getUserBySlug({ slug }) {
     console.log('Static method: getUserBySlug');
 
-    return this.findOne({ slug }, 'email displayName avatarUrl').lean();
+    return this.findOne({ slug }, 'email displayName avatarUrl').setOptions({ lean: true });
   }
 
   public static async updateProfile({ userId, name, avatarUrl }) {
@@ -69,7 +69,7 @@ class UserClass extends mongoose.Model {
 
     return this.findByIdAndUpdate(userId, { $set: modifier }, { new: true, runValidators: true })
       .select('displayName avatarUrl slug')
-      .lean();
+      .setOptions({ lean: true });
   }
 }
 
diff --git a/book/4-end/api/server/server.ts b/book/4-end/api/server/server.ts
index bbf5a9a0..ec3778cc 100644
--- a/book/4-end/api/server/server.ts
+++ b/book/4-end/api/server/server.ts
@@ -34,9 +34,6 @@ server.get('*', (_, res) => {
   res.sendStatus(403);
 });
 
-server.listen(process.env.PORT_API, (err) => {
-  if (err) {
-    throw err;
-  }
+server.listen(process.env.PORT_API, () => {
   console.log(`> Ready on ${process.env.URL_API}`);
 });
diff --git a/book/4-end/api/server/utils/slugify.ts b/book/4-end/api/server/utils/slugify.ts
index 9f970667..1a0b9d99 100644
--- a/book/4-end/api/server/utils/slugify.ts
+++ b/book/4-end/api/server/utils/slugify.ts
@@ -5,7 +5,7 @@ const slugify = (text) => _.kebabCase(text);
 async function createUniqueSlug(Model, slug, count, filter) {
   const obj = await Model.findOne({ slug: `${slug}-${count}`, ...filter })
     .select('_id')
-    .lean();
+    .setOptions({ lean: true });
 
   if (!obj) {
     return `${slug}-${count}`;
@@ -19,7 +19,7 @@ async function generateSlug(Model, name, filter = {}) {
 
   const obj = await Model.findOne({ slug: origSlug, ...filter })
     .select('_id')
-    .lean();
+    .setOptions({ lean: true });
 
   if (!obj) {
     return origSlug;
diff --git a/book/4-end/app/server/server.ts b/book/4-end/app/server/server.ts
index 01cfcf06..4d2bc446 100644
--- a/book/4-end/app/server/server.ts
+++ b/book/4-end/app/server/server.ts
@@ -26,10 +26,7 @@ app.prepare().then(() => {
     handle(req, res);
   });
 
-  server.listen(process.env.PORT_APP, (err) => {
-    if (err) {
-      throw err;
-    }
+  server.listen(process.env.PORT_APP, () => {
     console.log(`> Ready on ${process.env.URL_APP}`);
   });
 });
diff --git a/book/5-begin/api/server/aws-s3.ts b/book/5-begin/api/server/aws-s3.ts
index 81b9671c..302b4659 100644
--- a/book/5-begin/api/server/aws-s3.ts
+++ b/book/5-begin/api/server/aws-s3.ts
@@ -21,7 +21,7 @@ async function signRequestForUpload({ fileName, fileType, prefix, bucket }) {
 
   const s3 = new aws.S3({
     apiVersion: 'latest',
-    region: 'us-east-1',
+    region: process.env.AWS_REGION,
     accessKeyId: process.env.AWS_ACCESSKEYID,
     secretAccessKey: process.env.AWS_SECRETACCESSKEY,
   });
diff --git a/book/5-begin/api/server/models/User.ts b/book/5-begin/api/server/models/User.ts
index 0077c773..45c07d22 100644
--- a/book/5-begin/api/server/models/User.ts
+++ b/book/5-begin/api/server/models/User.ts
@@ -50,7 +50,7 @@ class UserClass extends mongoose.Model {
   public static async getUserBySlug({ slug }) {
     console.log('Static method: getUserBySlug');
 
-    return this.findOne({ slug }, 'email displayName avatarUrl').lean();
+    return this.findOne({ slug }, 'email displayName avatarUrl').setOptions({ lean: true });
   }
 
   public static async updateProfile({ userId, name, avatarUrl }) {
@@ -69,7 +69,7 @@ class UserClass extends mongoose.Model {
 
     return this.findByIdAndUpdate(userId, { $set: modifier }, { new: true, runValidators: true })
       .select('displayName avatarUrl slug')
-      .lean();
+      .setOptions({ lean: true });
   }
 }
 
diff --git a/book/5-begin/api/server/server.ts b/book/5-begin/api/server/server.ts
index bbf5a9a0..ec3778cc 100644
--- a/book/5-begin/api/server/server.ts
+++ b/book/5-begin/api/server/server.ts
@@ -34,9 +34,6 @@ server.get('*', (_, res) => {
   res.sendStatus(403);
 });
 
-server.listen(process.env.PORT_API, (err) => {
-  if (err) {
-    throw err;
-  }
+server.listen(process.env.PORT_API, () => {
   console.log(`> Ready on ${process.env.URL_API}`);
 });
diff --git a/book/5-begin/api/server/utils/slugify.ts b/book/5-begin/api/server/utils/slugify.ts
index 9f970667..1a0b9d99 100644
--- a/book/5-begin/api/server/utils/slugify.ts
+++ b/book/5-begin/api/server/utils/slugify.ts
@@ -5,7 +5,7 @@ const slugify = (text) => _.kebabCase(text);
 async function createUniqueSlug(Model, slug, count, filter) {
   const obj = await Model.findOne({ slug: `${slug}-${count}`, ...filter })
     .select('_id')
-    .lean();
+    .setOptions({ lean: true });
 
   if (!obj) {
     return `${slug}-${count}`;
@@ -19,7 +19,7 @@ async function generateSlug(Model, name, filter = {}) {
 
   const obj = await Model.findOne({ slug: origSlug, ...filter })
     .select('_id')
-    .lean();
+    .setOptions({ lean: true });
 
   if (!obj) {
     return origSlug;
diff --git a/book/5-begin/app/server/server.ts b/book/5-begin/app/server/server.ts
index 01cfcf06..4d2bc446 100644
--- a/book/5-begin/app/server/server.ts
+++ b/book/5-begin/app/server/server.ts
@@ -26,10 +26,7 @@ app.prepare().then(() => {
     handle(req, res);
   });
 
-  server.listen(process.env.PORT_APP, (err) => {
-    if (err) {
-      throw err;
-    }
+  server.listen(process.env.PORT_APP, () => {
     console.log(`> Ready on ${process.env.URL_APP}`);
   });
 });
diff --git a/book/5-end/api/server/aws-s3.ts b/book/5-end/api/server/aws-s3.ts
index 81b9671c..302b4659 100644
--- a/book/5-end/api/server/aws-s3.ts
+++ b/book/5-end/api/server/aws-s3.ts
@@ -21,7 +21,7 @@ async function signRequestForUpload({ fileName, fileType, prefix, bucket }) {
 
   const s3 = new aws.S3({
     apiVersion: 'latest',
-    region: 'us-east-1',
+    region: process.env.AWS_REGION,
     accessKeyId: process.env.AWS_ACCESSKEYID,
     secretAccessKey: process.env.AWS_SECRETACCESSKEY,
   });
diff --git a/book/5-end/api/server/models/User.ts b/book/5-end/api/server/models/User.ts
index 3444efe3..814785d3 100644
--- a/book/5-end/api/server/models/User.ts
+++ b/book/5-end/api/server/models/User.ts
@@ -81,7 +81,7 @@ class UserClass extends mongoose.Model {
   public static async getUserBySlug({ slug }) {
     console.log('Static method: getUserBySlug');
 
-    return this.findOne({ slug }, 'email displayName avatarUrl').lean();
+    return this.findOne({ slug }, 'email displayName avatarUrl').setOptions({ lean: true });
   }
 
   public static async updateProfile({ userId, name, avatarUrl }) {
@@ -100,7 +100,7 @@ class UserClass extends mongoose.Model {
 
     return this.findByIdAndUpdate(userId, { $set: modifier }, { new: true, runValidators: true })
       .select('displayName avatarUrl slug')
-      .lean();
+      .setOptions({ lean: true });
   }
 
   public static publicFields(): string[] {
@@ -116,7 +116,7 @@ class UserClass extends mongoose.Model {
   }) {
     const user = await this.findOne({ email })
       .select([...this.publicFields(), 'googleId'].join(' '))
-      .lean();
+      .setOptions({ lean: true });
 
     if (user) {
       if (_.isEmpty(googleToken) && user.googleId) {
diff --git a/book/5-end/api/server/server.ts b/book/5-end/api/server/server.ts
index eec116de..2b21ff4e 100644
--- a/book/5-end/api/server/server.ts
+++ b/book/5-end/api/server/server.ts
@@ -62,9 +62,6 @@ server.get('*', (_, res) => {
   res.sendStatus(403);
 });
 
-server.listen(process.env.PORT_API, (err) => {
-  if (err) {
-    throw err;
-  }
+server.listen(process.env.PORT_API, () => {
   console.log(`> Ready on ${process.env.URL_API}`);
 });
diff --git a/book/5-end/api/server/utils/slugify.ts b/book/5-end/api/server/utils/slugify.ts
index 9f970667..1a0b9d99 100644
--- a/book/5-end/api/server/utils/slugify.ts
+++ b/book/5-end/api/server/utils/slugify.ts
@@ -5,7 +5,7 @@ const slugify = (text) => _.kebabCase(text);
 async function createUniqueSlug(Model, slug, count, filter) {
   const obj = await Model.findOne({ slug: `${slug}-${count}`, ...filter })
     .select('_id')
-    .lean();
+    .setOptions({ lean: true });
 
   if (!obj) {
     return `${slug}-${count}`;
@@ -19,7 +19,7 @@ async function generateSlug(Model, name, filter = {}) {
 
   const obj = await Model.findOne({ slug: origSlug, ...filter })
     .select('_id')
-    .lean();
+    .setOptions({ lean: true });
 
   if (!obj) {
     return origSlug;
diff --git a/book/5-end/app/server/server.ts b/book/5-end/app/server/server.ts
index 01cfcf06..4d2bc446 100644
--- a/book/5-end/app/server/server.ts
+++ b/book/5-end/app/server/server.ts
@@ -26,10 +26,7 @@ app.prepare().then(() => {
     handle(req, res);
   });
 
-  server.listen(process.env.PORT_APP, (err) => {
-    if (err) {
-      throw err;
-    }
+  server.listen(process.env.PORT_APP, () => {
     console.log(`> Ready on ${process.env.URL_APP}`);
   });
 });
diff --git a/book/6-begin/api/server/aws-s3.ts b/book/6-begin/api/server/aws-s3.ts
index 81b9671c..302b4659 100644
--- a/book/6-begin/api/server/aws-s3.ts
+++ b/book/6-begin/api/server/aws-s3.ts
@@ -21,7 +21,7 @@ async function signRequestForUpload({ fileName, fileType, prefix, bucket }) {
 
   const s3 = new aws.S3({
     apiVersion: 'latest',
-    region: 'us-east-1',
+    region: process.env.AWS_REGION,
     accessKeyId: process.env.AWS_ACCESSKEYID,
     secretAccessKey: process.env.AWS_SECRETACCESSKEY,
   });
diff --git a/book/6-begin/api/server/models/User.ts b/book/6-begin/api/server/models/User.ts
index b801d1cc..34eb8f77 100644
--- a/book/6-begin/api/server/models/User.ts
+++ b/book/6-begin/api/server/models/User.ts
@@ -83,7 +83,7 @@ class UserClass extends mongoose.Model {
   public static async getUserBySlug({ slug }) {
     console.log('Static method: getUserBySlug');
 
-    return this.findOne({ slug }, 'email displayName avatarUrl').lean();
+    return this.findOne({ slug }, 'email displayName avatarUrl').setOptions({ lean: true });
   }
 
   public static async updateProfile({ userId, name, avatarUrl }) {
@@ -102,7 +102,7 @@ class UserClass extends mongoose.Model {
 
     return this.findByIdAndUpdate(userId, { $set: modifier }, { new: true, runValidators: true })
       .select('displayName avatarUrl slug')
-      .lean();
+      .setOptions({ lean: true });
   }
 
   public static publicFields(): string[] {
@@ -118,7 +118,7 @@ class UserClass extends mongoose.Model {
   }) {
     const user = await this.findOne({ email })
       .select([...this.publicFields(), 'googleId'].join(' '))
-      .lean();
+      .setOptions({ lean: true });
 
     if (user) {
       if (_.isEmpty(googleToken) && user.googleId) {
diff --git a/book/6-begin/api/server/server.ts b/book/6-begin/api/server/server.ts
index eec116de..2b21ff4e 100644
--- a/book/6-begin/api/server/server.ts
+++ b/book/6-begin/api/server/server.ts
@@ -62,9 +62,6 @@ server.get('*', (_, res) => {
   res.sendStatus(403);
 });
 
-server.listen(process.env.PORT_API, (err) => {
-  if (err) {
-    throw err;
-  }
+server.listen(process.env.PORT_API, () => {
   console.log(`> Ready on ${process.env.URL_API}`);
 });
diff --git a/book/6-begin/api/server/utils/slugify.ts b/book/6-begin/api/server/utils/slugify.ts
index 9f970667..1a0b9d99 100644
--- a/book/6-begin/api/server/utils/slugify.ts
+++ b/book/6-begin/api/server/utils/slugify.ts
@@ -5,7 +5,7 @@ const slugify = (text) => _.kebabCase(text);
 async function createUniqueSlug(Model, slug, count, filter) {
   const obj = await Model.findOne({ slug: `${slug}-${count}`, ...filter })
     .select('_id')
-    .lean();
+    .setOptions({ lean: true });
 
   if (!obj) {
     return `${slug}-${count}`;
@@ -19,7 +19,7 @@ async function generateSlug(Model, name, filter = {}) {
 
   const obj = await Model.findOne({ slug: origSlug, ...filter })
     .select('_id')
-    .lean();
+    .setOptions({ lean: true });
 
   if (!obj) {
     return origSlug;
diff --git a/book/6-begin/app/server/server.ts b/book/6-begin/app/server/server.ts
index 01cfcf06..4d2bc446 100644
--- a/book/6-begin/app/server/server.ts
+++ b/book/6-begin/app/server/server.ts
@@ -26,10 +26,7 @@ app.prepare().then(() => {
     handle(req, res);
   });
 
-  server.listen(process.env.PORT_APP, (err) => {
-    if (err) {
-      throw err;
-    }
+  server.listen(process.env.PORT_APP, () => {
     console.log(`> Ready on ${process.env.URL_APP}`);
   });
 });
diff --git a/book/6-end/api/server/aws-s3.ts b/book/6-end/api/server/aws-s3.ts
index 81b9671c..302b4659 100644
--- a/book/6-end/api/server/aws-s3.ts
+++ b/book/6-end/api/server/aws-s3.ts
@@ -21,7 +21,7 @@ async function signRequestForUpload({ fileName, fileType, prefix, bucket }) {
 
   const s3 = new aws.S3({
     apiVersion: 'latest',
-    region: 'us-east-1',
+    region: process.env.AWS_REGION,
     accessKeyId: process.env.AWS_ACCESSKEYID,
     secretAccessKey: process.env.AWS_SECRETACCESSKEY,
   });
diff --git a/book/6-end/api/server/aws-ses.ts b/book/6-end/api/server/aws-ses.ts
index faf399eb..fff1565e 100644
--- a/book/6-end/api/server/aws-ses.ts
+++ b/book/6-end/api/server/aws-ses.ts
@@ -3,7 +3,7 @@ import * as aws from 'aws-sdk';
 export default function sendEmail(options) {
   const ses = new aws.SES({
     apiVersion: 'latest',
-    region: 'us-east-1',
+    region: process.env.AWS_REGION,
     accessKeyId: process.env.AWS_ACCESSKEYID,
     secretAccessKey: process.env.AWS_SECRETACCESSKEY,
   });
diff --git a/book/6-end/api/server/models/EmailTemplate.ts b/book/6-end/api/server/models/EmailTemplate.ts
index 5f3c412c..eae337f1 100644
--- a/book/6-end/api/server/models/EmailTemplate.ts
+++ b/book/6-end/api/server/models/EmailTemplate.ts
@@ -58,7 +58,7 @@ export async function insertTemplates() {
   ];
 
   for (const t of templates) {
-    const et = await EmailTemplate.findOne({ name: t.name }).lean();
+    const et = await EmailTemplate.findOne({ name: t.name }).setOptions({ lean: true });
     const message = t.message.replace(/\n/g, '').replace(/[ ]+/g, ' ').trim();
 
     if (!et) {
@@ -72,7 +72,7 @@ export async function insertTemplates() {
 export default async function getEmailTemplate(name: string, params: any) {
   await insertTemplates();
 
-  const et = await EmailTemplate.findOne({ name }).lean();
+  const et = await EmailTemplate.findOne({ name }).setOptions({ lean: true });
 
   if (!et) {
     throw new Error('Email Template is not found in database.');
diff --git a/book/6-end/api/server/models/User.ts b/book/6-end/api/server/models/User.ts
index 09c676f9..aed09c95 100644
--- a/book/6-end/api/server/models/User.ts
+++ b/book/6-end/api/server/models/User.ts
@@ -94,7 +94,7 @@ class UserClass extends mongoose.Model {
   public static async getUserBySlug({ slug }) {
     console.log('Static method: getUserBySlug');
 
-    return this.findOne({ slug }, 'email displayName avatarUrl').lean();
+    return this.findOne({ slug }, 'email displayName avatarUrl').setOptions({ lean: true });
   }
 
   public static async updateProfile({ userId, name, avatarUrl }) {
@@ -113,7 +113,7 @@ class UserClass extends mongoose.Model {
 
     return this.findByIdAndUpdate(userId, { $set: modifier }, { new: true, runValidators: true })
       .select('displayName avatarUrl slug')
-      .lean();
+      .setOptions({ lean: true });
   }
 
   public static publicFields(): string[] {
@@ -129,7 +129,7 @@ class UserClass extends mongoose.Model {
   }) {
     const user = await this.findOne({ email })
       .select([...this.publicFields(), 'googleId'].join(' '))
-      .lean();
+      .setOptions({ lean: true });
 
     if (user) {
       if (_.isEmpty(googleToken) && user.googleId) {
@@ -190,7 +190,7 @@ class UserClass extends mongoose.Model {
   }
 
   public static async signInOrSignUpByPasswordless({ uid, email }) {
-    const user = await this.findOne({ email }).select(this.publicFields().join(' ')).lean();
+    const user = await this.findOne({ email }).select(this.publicFields().join(' ')).setOptions({ lean: true });
 
     if (user) {
       throw Error('User already exists');
diff --git a/book/6-end/api/server/passwordless-auth.ts b/book/6-end/api/server/passwordless-auth.ts
index 4674dc39..3c5e546b 100644
--- a/book/6-end/api/server/passwordless-auth.ts
+++ b/book/6-end/api/server/passwordless-auth.ts
@@ -49,7 +49,7 @@ function setupPasswordless({ server }) {
     '/auth/email-login-link',
     passwordless.requestToken(async (email, __, callback) => {
       try {
-        const user = await User.findOne({ email }).select('_id').lean();
+        const user = await User.findOne({ email }).select('_id').setOptions({ lean: true });
 
         if (user) {
           callback(null, user._id);
diff --git a/book/6-end/api/server/passwordless-token-mongostore.ts b/book/6-end/api/server/passwordless-token-mongostore.ts
index 55166cba..d6546e36 100644
--- a/book/6-end/api/server/passwordless-token-mongostore.ts
+++ b/book/6-end/api/server/passwordless-token-mongostore.ts
@@ -130,7 +130,7 @@ MongoStore.prototype.storeOrUpdateByEmail = async function addEmail(email: strin
     throw new Error('TokenStore:addEmail called with invalid parameters');
   }
 
-  const obj = await PasswordlessToken.findOne({ email }).select('uid').lean();
+  const obj = await PasswordlessToken.findOne({ email }).select('uid').setOptions({ lean: true });
 
   if (obj) {
     return obj.uid;
diff --git a/book/6-end/api/server/server.ts b/book/6-end/api/server/server.ts
index f84bdcde..6dc72f2d 100644
--- a/book/6-end/api/server/server.ts
+++ b/book/6-end/api/server/server.ts
@@ -68,9 +68,6 @@ server.get('*', (_, res) => {
   res.sendStatus(403);
 });
 
-server.listen(process.env.PORT_API, (err) => {
-  if (err) {
-    throw err;
-  }
+server.listen(process.env.PORT_API, () => {
   console.log(`> Ready on ${process.env.URL_API}`);
 });
diff --git a/book/6-end/api/server/utils/slugify.ts b/book/6-end/api/server/utils/slugify.ts
index 9f970667..1a0b9d99 100644
--- a/book/6-end/api/server/utils/slugify.ts
+++ b/book/6-end/api/server/utils/slugify.ts
@@ -5,7 +5,7 @@ const slugify = (text) => _.kebabCase(text);
 async function createUniqueSlug(Model, slug, count, filter) {
   const obj = await Model.findOne({ slug: `${slug}-${count}`, ...filter })
     .select('_id')
-    .lean();
+    .setOptions({ lean: true });
 
   if (!obj) {
     return `${slug}-${count}`;
@@ -19,7 +19,7 @@ async function generateSlug(Model, name, filter = {}) {
 
   const obj = await Model.findOne({ slug: origSlug, ...filter })
     .select('_id')
-    .lean();
+    .setOptions({ lean: true });
 
   if (!obj) {
     return origSlug;
diff --git a/book/6-end/app/server/server.ts b/book/6-end/app/server/server.ts
index 01cfcf06..4d2bc446 100644
--- a/book/6-end/app/server/server.ts
+++ b/book/6-end/app/server/server.ts
@@ -26,10 +26,7 @@ app.prepare().then(() => {
     handle(req, res);
   });
 
-  server.listen(process.env.PORT_APP, (err) => {
-    if (err) {
-      throw err;
-    }
+  server.listen(process.env.PORT_APP, () => {
     console.log(`> Ready on ${process.env.URL_APP}`);
   });
 });
diff --git a/book/7-begin/api/server/aws-s3.ts b/book/7-begin/api/server/aws-s3.ts
index 81b9671c..302b4659 100644
--- a/book/7-begin/api/server/aws-s3.ts
+++ b/book/7-begin/api/server/aws-s3.ts
@@ -21,7 +21,7 @@ async function signRequestForUpload({ fileName, fileType, prefix, bucket }) {
 
   const s3 = new aws.S3({
     apiVersion: 'latest',
-    region: 'us-east-1',
+    region: process.env.AWS_REGION,
     accessKeyId: process.env.AWS_ACCESSKEYID,
     secretAccessKey: process.env.AWS_SECRETACCESSKEY,
   });
diff --git a/book/7-begin/api/server/aws-ses.ts b/book/7-begin/api/server/aws-ses.ts
index faf399eb..fff1565e 100644
--- a/book/7-begin/api/server/aws-ses.ts
+++ b/book/7-begin/api/server/aws-ses.ts
@@ -3,7 +3,7 @@ import * as aws from 'aws-sdk';
 export default function sendEmail(options) {
   const ses = new aws.SES({
     apiVersion: 'latest',
-    region: 'us-east-1',
+    region: process.env.AWS_REGION,
     accessKeyId: process.env.AWS_ACCESSKEYID,
     secretAccessKey: process.env.AWS_SECRETACCESSKEY,
   });
diff --git a/book/7-begin/api/server/models/EmailTemplate.ts b/book/7-begin/api/server/models/EmailTemplate.ts
index 5f3c412c..eae337f1 100644
--- a/book/7-begin/api/server/models/EmailTemplate.ts
+++ b/book/7-begin/api/server/models/EmailTemplate.ts
@@ -58,7 +58,7 @@ export async function insertTemplates() {
   ];
 
   for (const t of templates) {
-    const et = await EmailTemplate.findOne({ name: t.name }).lean();
+    const et = await EmailTemplate.findOne({ name: t.name }).setOptions({ lean: true });
     const message = t.message.replace(/\n/g, '').replace(/[ ]+/g, ' ').trim();
 
     if (!et) {
@@ -72,7 +72,7 @@ export async function insertTemplates() {
 export default async function getEmailTemplate(name: string, params: any) {
   await insertTemplates();
 
-  const et = await EmailTemplate.findOne({ name }).lean();
+  const et = await EmailTemplate.findOne({ name }).setOptions({ lean: true });
 
   if (!et) {
     throw new Error('Email Template is not found in database.');
diff --git a/book/7-begin/api/server/models/User.ts b/book/7-begin/api/server/models/User.ts
index 09c676f9..aed09c95 100644
--- a/book/7-begin/api/server/models/User.ts
+++ b/book/7-begin/api/server/models/User.ts
@@ -94,7 +94,7 @@ class UserClass extends mongoose.Model {
   public static async getUserBySlug({ slug }) {
     console.log('Static method: getUserBySlug');
 
-    return this.findOne({ slug }, 'email displayName avatarUrl').lean();
+    return this.findOne({ slug }, 'email displayName avatarUrl').setOptions({ lean: true });
   }
 
   public static async updateProfile({ userId, name, avatarUrl }) {
@@ -113,7 +113,7 @@ class UserClass extends mongoose.Model {
 
     return this.findByIdAndUpdate(userId, { $set: modifier }, { new: true, runValidators: true })
       .select('displayName avatarUrl slug')
-      .lean();
+      .setOptions({ lean: true });
   }
 
   public static publicFields(): string[] {
@@ -129,7 +129,7 @@ class UserClass extends mongoose.Model {
   }) {
     const user = await this.findOne({ email })
       .select([...this.publicFields(), 'googleId'].join(' '))
-      .lean();
+      .setOptions({ lean: true });
 
     if (user) {
       if (_.isEmpty(googleToken) && user.googleId) {
@@ -190,7 +190,7 @@ class UserClass extends mongoose.Model {
   }
 
   public static async signInOrSignUpByPasswordless({ uid, email }) {
-    const user = await this.findOne({ email }).select(this.publicFields().join(' ')).lean();
+    const user = await this.findOne({ email }).select(this.publicFields().join(' ')).setOptions({ lean: true });
 
     if (user) {
       throw Error('User already exists');
diff --git a/book/7-begin/api/server/passwordless-auth.ts b/book/7-begin/api/server/passwordless-auth.ts
index 4674dc39..3c5e546b 100644
--- a/book/7-begin/api/server/passwordless-auth.ts
+++ b/book/7-begin/api/server/passwordless-auth.ts
@@ -49,7 +49,7 @@ function setupPasswordless({ server }) {
     '/auth/email-login-link',
     passwordless.requestToken(async (email, __, callback) => {
       try {
-        const user = await User.findOne({ email }).select('_id').lean();
+        const user = await User.findOne({ email }).select('_id').setOptions({ lean: true });
 
         if (user) {
           callback(null, user._id);
diff --git a/book/7-begin/api/server/passwordless-token-mongostore.ts b/book/7-begin/api/server/passwordless-token-mongostore.ts
index 55166cba..d6546e36 100644
--- a/book/7-begin/api/server/passwordless-token-mongostore.ts
+++ b/book/7-begin/api/server/passwordless-token-mongostore.ts
@@ -130,7 +130,7 @@ MongoStore.prototype.storeOrUpdateByEmail = async function addEmail(email: strin
     throw new Error('TokenStore:addEmail called with invalid parameters');
   }
 
-  const obj = await PasswordlessToken.findOne({ email }).select('uid').lean();
+  const obj = await PasswordlessToken.findOne({ email }).select('uid').setOptions({ lean: true });
 
   if (obj) {
     return obj.uid;
diff --git a/book/7-begin/api/server/server.ts b/book/7-begin/api/server/server.ts
index 4f51bd98..955ed9fa 100644
--- a/book/7-begin/api/server/server.ts
+++ b/book/7-begin/api/server/server.ts
@@ -64,9 +64,6 @@ server.get('*', (_, res) => {
   res.sendStatus(403);
 });
 
-server.listen(process.env.PORT_API, (err) => {
-  if (err) {
-    throw err;
-  }
+server.listen(process.env.PORT_API, () => {
   console.log(`> Ready on ${process.env.URL_API}`);
 });
diff --git a/book/7-begin/api/server/utils/slugify.ts b/book/7-begin/api/server/utils/slugify.ts
index 9f970667..1a0b9d99 100644
--- a/book/7-begin/api/server/utils/slugify.ts
+++ b/book/7-begin/api/server/utils/slugify.ts
@@ -5,7 +5,7 @@ const slugify = (text) => _.kebabCase(text);
 async function createUniqueSlug(Model, slug, count, filter) {
   const obj = await Model.findOne({ slug: `${slug}-${count}`, ...filter })
     .select('_id')
-    .lean();
+    .setOptions({ lean: true });
 
   if (!obj) {
     return `${slug}-${count}`;
@@ -19,7 +19,7 @@ async function generateSlug(Model, name, filter = {}) {
 
   const obj = await Model.findOne({ slug: origSlug, ...filter })
     .select('_id')
-    .lean();
+    .setOptions({ lean: true });
 
   if (!obj) {
     return origSlug;
diff --git a/book/7-begin/app/server/server.ts b/book/7-begin/app/server/server.ts
index 01cfcf06..4d2bc446 100644
--- a/book/7-begin/app/server/server.ts
+++ b/book/7-begin/app/server/server.ts
@@ -26,10 +26,7 @@ app.prepare().then(() => {
     handle(req, res);
   });
 
-  server.listen(process.env.PORT_APP, (err) => {
-    if (err) {
-      throw err;
-    }
+  server.listen(process.env.PORT_APP, () => {
     console.log(`> Ready on ${process.env.URL_APP}`);
   });
 });
diff --git a/book/7-end/api/server/aws-s3.ts b/book/7-end/api/server/aws-s3.ts
index 6d50475b..bf432d48 100644
--- a/book/7-end/api/server/aws-s3.ts
+++ b/book/7-end/api/server/aws-s3.ts
@@ -21,7 +21,7 @@ async function signRequestForUpload({ fileName, fileType, prefix, bucket }) {
 
   const s3 = new aws.S3({
     apiVersion: 'latest',
-    region: 'us-east-1',
+    region: process.env.AWS_REGION,
     accessKeyId: process.env.AWS_ACCESSKEYID,
     secretAccessKey: process.env.AWS_SECRETACCESSKEY,
   });
diff --git a/book/7-end/api/server/aws-ses.ts b/book/7-end/api/server/aws-ses.ts
index faf399eb..fff1565e 100644
--- a/book/7-end/api/server/aws-ses.ts
+++ b/book/7-end/api/server/aws-ses.ts
@@ -3,7 +3,7 @@ import * as aws from 'aws-sdk';
 export default function sendEmail(options) {
   const ses = new aws.SES({
     apiVersion: 'latest',
-    region: 'us-east-1',
+    region: process.env.AWS_REGION,
     accessKeyId: process.env.AWS_ACCESSKEYID,
     secretAccessKey: process.env.AWS_SECRETACCESSKEY,
   });
diff --git a/book/7-end/api/server/models/EmailTemplate.ts b/book/7-end/api/server/models/EmailTemplate.ts
index fb8ae2e6..44cb9648 100644
--- a/book/7-end/api/server/models/EmailTemplate.ts
+++ b/book/7-end/api/server/models/EmailTemplate.ts
@@ -74,7 +74,7 @@ export async function insertTemplates() {
   ];
 
   for (const t of templates) {
-    const et = await EmailTemplate.findOne({ name: t.name }).lean();
+    const et = await EmailTemplate.findOne({ name: t.name }).setOptions({ lean: true });
     const message = t.message.replace(/\n/g, '').replace(/[ ]+/g, ' ').trim();
 
     if (!et) {
@@ -88,7 +88,7 @@ export async function insertTemplates() {
 export default async function getEmailTemplate(name: string, params: any) {
   await insertTemplates();
 
-  const et = await EmailTemplate.findOne({ name }).lean();
+  const et = await EmailTemplate.findOne({ name }).setOptions({ lean: true });
 
   if (!et) {
     throw new Error('Email Template is not found in database.');
diff --git a/book/7-end/api/server/models/Invitation.ts b/book/7-end/api/server/models/Invitation.ts
index c1d15471..60cd8dcf 100644
--- a/book/7-end/api/server/models/Invitation.ts
+++ b/book/7-end/api/server/models/Invitation.ts
@@ -68,12 +68,12 @@ class InvitationClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const team = await Team.findById(teamId).lean();
+    const team = await Team.findById(teamId).setOptions({ lean: true });
     if (!team || team.teamLeaderId !== userId) {
       throw new Error('Team does not exist or you have no permission');
     }
 
-    const registeredUser = await User.findOne({ email }).select('defaultTeamSlug').lean();
+    const registeredUser = await User.findOne({ email }).select('defaultTeamSlug').setOptions({ lean: true });
 
     if (registeredUser) {
       if (team.memberIds.includes(registeredUser._id.toString())) {
@@ -90,7 +90,7 @@ class InvitationClass extends mongoose.Model {
     }
 
     let token;
-    const invitation = await this.findOne({ teamId, email }).select('token').lean();
+    const invitation = await this.findOne({ teamId, email }).select('token').setOptions({ lean: true });
 
     if (invitation) {
       token = invitation.token;
@@ -125,17 +125,17 @@ class InvitationClass extends mongoose.Model {
       console.log('Email sending error:', err);
     });
 
-    return await this.findOne({ teamId, email }).lean();
+    return await this.findOne({ teamId, email }).setOptions({ lean: true });
   }
 
   public static async getTeamInvitations({ userId, teamId }) {
-    const team = await Team.findOne({ _id: teamId }).select('teamLeaderId').lean();
+    const team = await Team.findOne({ _id: teamId }).select('teamLeaderId').setOptions({ lean: true });
 
     if (userId !== team.teamLeaderId) {
       throw new Error('You have no permission.');
     }
 
-    return this.find({ teamId }).select('email').lean();
+    return this.find({ teamId }).select('email').setOptions({ lean: true });
   }
 
   public static async getTeamByToken({ token }) {
@@ -143,7 +143,7 @@ class InvitationClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const invitation = await this.findOne({ token }).lean();
+    const invitation = await this.findOne({ token }).setOptions({ lean: true });
 
     if (!invitation) {
       throw new Error('Invitation not found');
@@ -151,7 +151,7 @@ class InvitationClass extends mongoose.Model {
 
     const team = await Team.findById(invitation.teamId)
       .select('name slug avatarUrl memberIds')
-      .lean();
+      .setOptions({ lean: true });
 
     if (!team) {
       throw new Error('Team does not exist');
@@ -165,7 +165,7 @@ class InvitationClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const invitation = await this.findOne({ token }).lean();
+    const invitation = await this.findOne({ token }).setOptions({ lean: true });
 
     if (!invitation) {
       throw new Error('Invitation not found');
@@ -173,7 +173,7 @@ class InvitationClass extends mongoose.Model {
 
     const team = await Team.findById(invitation.teamId)
       .select('name slug avatarUrl memberIds')
-      .lean();
+      .setOptions({ lean: true });
 
     if (!team) {
       throw new Error('Team does not exist');
@@ -189,7 +189,7 @@ class InvitationClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const invitation = await this.findOne({ token }).lean();
+    const invitation = await this.findOne({ token }).setOptions({ lean: true });
 
     if (!invitation || invitation.email !== user.email) {
       throw new Error('Invitation not found');
@@ -199,7 +199,7 @@ class InvitationClass extends mongoose.Model {
 
     const team = await Team.findById(invitation.teamId)
       .select('memberIds slug teamLeaderId')
-      .lean();
+      .setOptions({ lean: true });
 
     if (!team) {
       throw new Error('Team does not exist');
diff --git a/book/7-end/api/server/models/Team.ts b/book/7-end/api/server/models/Team.ts
index f26f9e7f..37697b26 100644
--- a/book/7-end/api/server/models/Team.ts
+++ b/book/7-end/api/server/models/Team.ts
@@ -24,10 +24,12 @@ const mongoSchema = new mongoose.Schema({
     type: String,
     required: true,
   },
-  memberIds: {
-    type: [String],
-    required: true,
-  },
+  memberIds: [
+    {
+      type: String,
+      required: true,
+    },
+  ],
   defaultTeam: {
     type: Boolean,
     default: false,
@@ -128,12 +130,12 @@ class TeamClass extends mongoose.Model {
 
     await this.updateOne({ _id: teamId }, { $set: modifier }, { runValidators: true });
 
-    return this.findById(teamId, 'name avatarUrl slug defaultTeam').lean();
+    return this.findById(teamId, 'name avatarUrl slug defaultTeam').setOptions({ lean: true });
   }
 
   public static getAllTeamsForUser(userId: string) {
     console.log(`userId:${userId}`);
-    return this.find({ memberIds: userId }).lean();
+    return this.find({ memberIds: userId }).setOptions({ lean: true });
   }
 
   public static async removeMember({ teamId, teamLeaderId, userId }) {
diff --git a/book/7-end/api/server/models/User.ts b/book/7-end/api/server/models/User.ts
index 3ea37d04..62dc091d 100644
--- a/book/7-end/api/server/models/User.ts
+++ b/book/7-end/api/server/models/User.ts
@@ -120,7 +120,7 @@ class UserClass extends mongoose.Model {
   public static async getUserBySlug({ slug }) {
     console.log('Static method: getUserBySlug');
 
-    return this.findOne({ slug }, 'email displayName avatarUrl').lean();
+    return this.findOne({ slug }, 'email displayName avatarUrl').setOptions({ lean: true });
   }
 
   public static async updateProfile({ userId, name, avatarUrl }) {
@@ -139,7 +139,7 @@ class UserClass extends mongoose.Model {
 
     return this.findByIdAndUpdate(userId, { $set: modifier }, { new: true, runValidators: true })
       .select('displayName avatarUrl slug')
-      .lean();
+      .setOptions({ lean: true });
   }
 
   public static publicFields(): string[] {
@@ -165,7 +165,7 @@ class UserClass extends mongoose.Model {
   }) {
     const user = await this.findOne({ email })
       .select([...this.publicFields(), 'googleId'].join(' '))
-      .lean();
+      .setOptions({ lean: true });
 
     if (user) {
       if (_.isEmpty(googleToken) && user.googleId) {
@@ -227,7 +227,7 @@ class UserClass extends mongoose.Model {
   }
 
   public static async signInOrSignUpByPasswordless({ uid, email }) {
-    const user = await this.findOne({ email }).select(this.publicFields().join(' ')).lean();
+    const user = await this.findOne({ email }).select(this.publicFields().join(' ')).setOptions({ lean: true });
 
     if (user) {
       throw Error('User already exists');
@@ -278,7 +278,7 @@ class UserClass extends mongoose.Model {
 
     return this.find({ _id: { $in: team.memberIds } })
       .select(this.publicFields().join(' '))
-      .lean();
+      .setOptions({ lean: true });
   }
 
   private static async checkPermissionAndGetTeam({ userId, teamId }) {
@@ -288,7 +288,7 @@ class UserClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const team = await Team.findById(teamId).select('memberIds').lean();
+    const team = await Team.findById(teamId).select('memberIds').setOptions({ lean: true });
 
     if (!team || team.memberIds.indexOf(userId) === -1) {
       throw new Error('Team not found');
diff --git a/book/7-end/api/server/passwordless-auth.ts b/book/7-end/api/server/passwordless-auth.ts
index b6e8b605..7b05d7b5 100644
--- a/book/7-end/api/server/passwordless-auth.ts
+++ b/book/7-end/api/server/passwordless-auth.ts
@@ -50,7 +50,7 @@ function setupPasswordless({ server }) {
     '/auth/email-login-link',
     passwordless.requestToken(async (email, __, callback) => {
       try {
-        const user = await User.findOne({ email }).select('_id').lean();
+        const user = await User.findOne({ email }).select('_id').setOptions({ lean: true });
 
         if (user) {
           callback(null, user._id);
diff --git a/book/7-end/api/server/passwordless-token-mongostore.ts b/book/7-end/api/server/passwordless-token-mongostore.ts
index 55166cba..d6546e36 100644
--- a/book/7-end/api/server/passwordless-token-mongostore.ts
+++ b/book/7-end/api/server/passwordless-token-mongostore.ts
@@ -130,7 +130,7 @@ MongoStore.prototype.storeOrUpdateByEmail = async function addEmail(email: strin
     throw new Error('TokenStore:addEmail called with invalid parameters');
   }
 
-  const obj = await PasswordlessToken.findOne({ email }).select('uid').lean();
+  const obj = await PasswordlessToken.findOne({ email }).select('uid').setOptions({ lean: true });
 
   if (obj) {
     return obj.uid;
diff --git a/book/7-end/api/server/server.ts b/book/7-end/api/server/server.ts
index 4f51bd98..955ed9fa 100644
--- a/book/7-end/api/server/server.ts
+++ b/book/7-end/api/server/server.ts
@@ -64,9 +64,6 @@ server.get('*', (_, res) => {
   res.sendStatus(403);
 });
 
-server.listen(process.env.PORT_API, (err) => {
-  if (err) {
-    throw err;
-  }
+server.listen(process.env.PORT_API, () => {
   console.log(`> Ready on ${process.env.URL_API}`);
 });
diff --git a/book/7-end/api/server/utils/slugify.ts b/book/7-end/api/server/utils/slugify.ts
index e76af3c6..f2394edd 100644
--- a/book/7-end/api/server/utils/slugify.ts
+++ b/book/7-end/api/server/utils/slugify.ts
@@ -5,7 +5,7 @@ const slugify = (text) => _.kebabCase(text);
 async function createUniqueSlug(Model, slug, count, filter) {
   const obj = await Model.findOne({ slug: `${slug}-${count}`, ...filter })
     .select('_id')
-    .lean();
+    .setOptions({ lean: true });
 
   if (!obj) {
     return `${slug}-${count}`;
@@ -19,7 +19,7 @@ async function generateSlug(Model, name, filter = {}) {
 
   const obj = await Model.findOne({ slug: origSlug, ...filter })
     .select('_id')
-    .lean();
+    .setOptions({ lean: true });
 
   if (!obj) {
     return origSlug;
@@ -31,7 +31,7 @@ async function generateSlug(Model, name, filter = {}) {
 async function generateNumberSlug(Model, filter = {}, n = 1) {
   const obj = await Model.findOne({ slug: n, ...filter })
     .select('_id')
-    .lean();
+    .setOptions({ lean: true });
 
   if (!obj) {
     return `${n}`;
diff --git a/book/7-end/app/server/server.ts b/book/7-end/app/server/server.ts
index e8849294..55d01719 100644
--- a/book/7-end/app/server/server.ts
+++ b/book/7-end/app/server/server.ts
@@ -31,10 +31,7 @@ app.prepare().then(() => {
     handle(req, res);
   });
 
-  server.listen(process.env.PORT_APP, (err) => {
-    if (err) {
-      throw err;
-    }
+  server.listen(process.env.PORT_APP, () => {
     console.log(`> Ready on ${process.env.URL_APP}`);
   });
 });
diff --git a/book/8-begin/api/server/aws-s3.ts b/book/8-begin/api/server/aws-s3.ts
index 6d50475b..bf432d48 100644
--- a/book/8-begin/api/server/aws-s3.ts
+++ b/book/8-begin/api/server/aws-s3.ts
@@ -21,7 +21,7 @@ async function signRequestForUpload({ fileName, fileType, prefix, bucket }) {
 
   const s3 = new aws.S3({
     apiVersion: 'latest',
-    region: 'us-east-1',
+    region: process.env.AWS_REGION,
     accessKeyId: process.env.AWS_ACCESSKEYID,
     secretAccessKey: process.env.AWS_SECRETACCESSKEY,
   });
diff --git a/book/8-begin/api/server/aws-ses.ts b/book/8-begin/api/server/aws-ses.ts
index faf399eb..fff1565e 100644
--- a/book/8-begin/api/server/aws-ses.ts
+++ b/book/8-begin/api/server/aws-ses.ts
@@ -3,7 +3,7 @@ import * as aws from 'aws-sdk';
 export default function sendEmail(options) {
   const ses = new aws.SES({
     apiVersion: 'latest',
-    region: 'us-east-1',
+    region: process.env.AWS_REGION,
     accessKeyId: process.env.AWS_ACCESSKEYID,
     secretAccessKey: process.env.AWS_SECRETACCESSKEY,
   });
diff --git a/book/8-begin/api/server/models/EmailTemplate.ts b/book/8-begin/api/server/models/EmailTemplate.ts
index fb8ae2e6..44cb9648 100644
--- a/book/8-begin/api/server/models/EmailTemplate.ts
+++ b/book/8-begin/api/server/models/EmailTemplate.ts
@@ -74,7 +74,7 @@ export async function insertTemplates() {
   ];
 
   for (const t of templates) {
-    const et = await EmailTemplate.findOne({ name: t.name }).lean();
+    const et = await EmailTemplate.findOne({ name: t.name }).setOptions({ lean: true });
     const message = t.message.replace(/\n/g, '').replace(/[ ]+/g, ' ').trim();
 
     if (!et) {
@@ -88,7 +88,7 @@ export async function insertTemplates() {
 export default async function getEmailTemplate(name: string, params: any) {
   await insertTemplates();
 
-  const et = await EmailTemplate.findOne({ name }).lean();
+  const et = await EmailTemplate.findOne({ name }).setOptions({ lean: true });
 
   if (!et) {
     throw new Error('Email Template is not found in database.');
diff --git a/book/8-begin/api/server/models/Invitation.ts b/book/8-begin/api/server/models/Invitation.ts
index c1d15471..60cd8dcf 100644
--- a/book/8-begin/api/server/models/Invitation.ts
+++ b/book/8-begin/api/server/models/Invitation.ts
@@ -68,12 +68,12 @@ class InvitationClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const team = await Team.findById(teamId).lean();
+    const team = await Team.findById(teamId).setOptions({ lean: true });
     if (!team || team.teamLeaderId !== userId) {
       throw new Error('Team does not exist or you have no permission');
     }
 
-    const registeredUser = await User.findOne({ email }).select('defaultTeamSlug').lean();
+    const registeredUser = await User.findOne({ email }).select('defaultTeamSlug').setOptions({ lean: true });
 
     if (registeredUser) {
       if (team.memberIds.includes(registeredUser._id.toString())) {
@@ -90,7 +90,7 @@ class InvitationClass extends mongoose.Model {
     }
 
     let token;
-    const invitation = await this.findOne({ teamId, email }).select('token').lean();
+    const invitation = await this.findOne({ teamId, email }).select('token').setOptions({ lean: true });
 
     if (invitation) {
       token = invitation.token;
@@ -125,17 +125,17 @@ class InvitationClass extends mongoose.Model {
       console.log('Email sending error:', err);
     });
 
-    return await this.findOne({ teamId, email }).lean();
+    return await this.findOne({ teamId, email }).setOptions({ lean: true });
   }
 
   public static async getTeamInvitations({ userId, teamId }) {
-    const team = await Team.findOne({ _id: teamId }).select('teamLeaderId').lean();
+    const team = await Team.findOne({ _id: teamId }).select('teamLeaderId').setOptions({ lean: true });
 
     if (userId !== team.teamLeaderId) {
       throw new Error('You have no permission.');
     }
 
-    return this.find({ teamId }).select('email').lean();
+    return this.find({ teamId }).select('email').setOptions({ lean: true });
   }
 
   public static async getTeamByToken({ token }) {
@@ -143,7 +143,7 @@ class InvitationClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const invitation = await this.findOne({ token }).lean();
+    const invitation = await this.findOne({ token }).setOptions({ lean: true });
 
     if (!invitation) {
       throw new Error('Invitation not found');
@@ -151,7 +151,7 @@ class InvitationClass extends mongoose.Model {
 
     const team = await Team.findById(invitation.teamId)
       .select('name slug avatarUrl memberIds')
-      .lean();
+      .setOptions({ lean: true });
 
     if (!team) {
       throw new Error('Team does not exist');
@@ -165,7 +165,7 @@ class InvitationClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const invitation = await this.findOne({ token }).lean();
+    const invitation = await this.findOne({ token }).setOptions({ lean: true });
 
     if (!invitation) {
       throw new Error('Invitation not found');
@@ -173,7 +173,7 @@ class InvitationClass extends mongoose.Model {
 
     const team = await Team.findById(invitation.teamId)
       .select('name slug avatarUrl memberIds')
-      .lean();
+      .setOptions({ lean: true });
 
     if (!team) {
       throw new Error('Team does not exist');
@@ -189,7 +189,7 @@ class InvitationClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const invitation = await this.findOne({ token }).lean();
+    const invitation = await this.findOne({ token }).setOptions({ lean: true });
 
     if (!invitation || invitation.email !== user.email) {
       throw new Error('Invitation not found');
@@ -199,7 +199,7 @@ class InvitationClass extends mongoose.Model {
 
     const team = await Team.findById(invitation.teamId)
       .select('memberIds slug teamLeaderId')
-      .lean();
+      .setOptions({ lean: true });
 
     if (!team) {
       throw new Error('Team does not exist');
diff --git a/book/8-begin/api/server/models/Team.ts b/book/8-begin/api/server/models/Team.ts
index f26f9e7f..37697b26 100644
--- a/book/8-begin/api/server/models/Team.ts
+++ b/book/8-begin/api/server/models/Team.ts
@@ -24,10 +24,12 @@ const mongoSchema = new mongoose.Schema({
     type: String,
     required: true,
   },
-  memberIds: {
-    type: [String],
-    required: true,
-  },
+  memberIds: [
+    {
+      type: String,
+      required: true,
+    },
+  ],
   defaultTeam: {
     type: Boolean,
     default: false,
@@ -128,12 +130,12 @@ class TeamClass extends mongoose.Model {
 
     await this.updateOne({ _id: teamId }, { $set: modifier }, { runValidators: true });
 
-    return this.findById(teamId, 'name avatarUrl slug defaultTeam').lean();
+    return this.findById(teamId, 'name avatarUrl slug defaultTeam').setOptions({ lean: true });
   }
 
   public static getAllTeamsForUser(userId: string) {
     console.log(`userId:${userId}`);
-    return this.find({ memberIds: userId }).lean();
+    return this.find({ memberIds: userId }).setOptions({ lean: true });
   }
 
   public static async removeMember({ teamId, teamLeaderId, userId }) {
diff --git a/book/8-begin/api/server/models/User.ts b/book/8-begin/api/server/models/User.ts
index 3ea37d04..62dc091d 100644
--- a/book/8-begin/api/server/models/User.ts
+++ b/book/8-begin/api/server/models/User.ts
@@ -120,7 +120,7 @@ class UserClass extends mongoose.Model {
   public static async getUserBySlug({ slug }) {
     console.log('Static method: getUserBySlug');
 
-    return this.findOne({ slug }, 'email displayName avatarUrl').lean();
+    return this.findOne({ slug }, 'email displayName avatarUrl').setOptions({ lean: true });
   }
 
   public static async updateProfile({ userId, name, avatarUrl }) {
@@ -139,7 +139,7 @@ class UserClass extends mongoose.Model {
 
     return this.findByIdAndUpdate(userId, { $set: modifier }, { new: true, runValidators: true })
       .select('displayName avatarUrl slug')
-      .lean();
+      .setOptions({ lean: true });
   }
 
   public static publicFields(): string[] {
@@ -165,7 +165,7 @@ class UserClass extends mongoose.Model {
   }) {
     const user = await this.findOne({ email })
       .select([...this.publicFields(), 'googleId'].join(' '))
-      .lean();
+      .setOptions({ lean: true });
 
     if (user) {
       if (_.isEmpty(googleToken) && user.googleId) {
@@ -227,7 +227,7 @@ class UserClass extends mongoose.Model {
   }
 
   public static async signInOrSignUpByPasswordless({ uid, email }) {
-    const user = await this.findOne({ email }).select(this.publicFields().join(' ')).lean();
+    const user = await this.findOne({ email }).select(this.publicFields().join(' ')).setOptions({ lean: true });
 
     if (user) {
       throw Error('User already exists');
@@ -278,7 +278,7 @@ class UserClass extends mongoose.Model {
 
     return this.find({ _id: { $in: team.memberIds } })
       .select(this.publicFields().join(' '))
-      .lean();
+      .setOptions({ lean: true });
   }
 
   private static async checkPermissionAndGetTeam({ userId, teamId }) {
@@ -288,7 +288,7 @@ class UserClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const team = await Team.findById(teamId).select('memberIds').lean();
+    const team = await Team.findById(teamId).select('memberIds').setOptions({ lean: true });
 
     if (!team || team.memberIds.indexOf(userId) === -1) {
       throw new Error('Team not found');
diff --git a/book/8-begin/api/server/passwordless-auth.ts b/book/8-begin/api/server/passwordless-auth.ts
index b6e8b605..7b05d7b5 100644
--- a/book/8-begin/api/server/passwordless-auth.ts
+++ b/book/8-begin/api/server/passwordless-auth.ts
@@ -50,7 +50,7 @@ function setupPasswordless({ server }) {
     '/auth/email-login-link',
     passwordless.requestToken(async (email, __, callback) => {
       try {
-        const user = await User.findOne({ email }).select('_id').lean();
+        const user = await User.findOne({ email }).select('_id').setOptions({ lean: true });
 
         if (user) {
           callback(null, user._id);
diff --git a/book/8-begin/api/server/passwordless-token-mongostore.ts b/book/8-begin/api/server/passwordless-token-mongostore.ts
index 55166cba..d6546e36 100644
--- a/book/8-begin/api/server/passwordless-token-mongostore.ts
+++ b/book/8-begin/api/server/passwordless-token-mongostore.ts
@@ -130,7 +130,7 @@ MongoStore.prototype.storeOrUpdateByEmail = async function addEmail(email: strin
     throw new Error('TokenStore:addEmail called with invalid parameters');
   }
 
-  const obj = await PasswordlessToken.findOne({ email }).select('uid').lean();
+  const obj = await PasswordlessToken.findOne({ email }).select('uid').setOptions({ lean: true });
 
   if (obj) {
     return obj.uid;
diff --git a/book/8-begin/api/server/server.ts b/book/8-begin/api/server/server.ts
index 4f51bd98..955ed9fa 100644
--- a/book/8-begin/api/server/server.ts
+++ b/book/8-begin/api/server/server.ts
@@ -64,9 +64,6 @@ server.get('*', (_, res) => {
   res.sendStatus(403);
 });
 
-server.listen(process.env.PORT_API, (err) => {
-  if (err) {
-    throw err;
-  }
+server.listen(process.env.PORT_API, () => {
   console.log(`> Ready on ${process.env.URL_API}`);
 });
diff --git a/book/8-begin/api/server/utils/slugify.ts b/book/8-begin/api/server/utils/slugify.ts
index e76af3c6..f2394edd 100644
--- a/book/8-begin/api/server/utils/slugify.ts
+++ b/book/8-begin/api/server/utils/slugify.ts
@@ -5,7 +5,7 @@ const slugify = (text) => _.kebabCase(text);
 async function createUniqueSlug(Model, slug, count, filter) {
   const obj = await Model.findOne({ slug: `${slug}-${count}`, ...filter })
     .select('_id')
-    .lean();
+    .setOptions({ lean: true });
 
   if (!obj) {
     return `${slug}-${count}`;
@@ -19,7 +19,7 @@ async function generateSlug(Model, name, filter = {}) {
 
   const obj = await Model.findOne({ slug: origSlug, ...filter })
     .select('_id')
-    .lean();
+    .setOptions({ lean: true });
 
   if (!obj) {
     return origSlug;
@@ -31,7 +31,7 @@ async function generateSlug(Model, name, filter = {}) {
 async function generateNumberSlug(Model, filter = {}, n = 1) {
   const obj = await Model.findOne({ slug: n, ...filter })
     .select('_id')
-    .lean();
+    .setOptions({ lean: true });
 
   if (!obj) {
     return `${n}`;
diff --git a/book/8-begin/app/server/server.ts b/book/8-begin/app/server/server.ts
index e8849294..55d01719 100644
--- a/book/8-begin/app/server/server.ts
+++ b/book/8-begin/app/server/server.ts
@@ -31,10 +31,7 @@ app.prepare().then(() => {
     handle(req, res);
   });
 
-  server.listen(process.env.PORT_APP, (err) => {
-    if (err) {
-      throw err;
-    }
+  server.listen(process.env.PORT_APP, () => {
     console.log(`> Ready on ${process.env.URL_APP}`);
   });
 });
diff --git a/book/8-end/api/server/aws-s3.ts b/book/8-end/api/server/aws-s3.ts
index 6d50475b..bf432d48 100644
--- a/book/8-end/api/server/aws-s3.ts
+++ b/book/8-end/api/server/aws-s3.ts
@@ -21,7 +21,7 @@ async function signRequestForUpload({ fileName, fileType, prefix, bucket }) {
 
   const s3 = new aws.S3({
     apiVersion: 'latest',
-    region: 'us-east-1',
+    region: process.env.AWS_REGION,
     accessKeyId: process.env.AWS_ACCESSKEYID,
     secretAccessKey: process.env.AWS_SECRETACCESSKEY,
   });
diff --git a/book/8-end/api/server/aws-ses.ts b/book/8-end/api/server/aws-ses.ts
index faf399eb..fff1565e 100644
--- a/book/8-end/api/server/aws-ses.ts
+++ b/book/8-end/api/server/aws-ses.ts
@@ -3,7 +3,7 @@ import * as aws from 'aws-sdk';
 export default function sendEmail(options) {
   const ses = new aws.SES({
     apiVersion: 'latest',
-    region: 'us-east-1',
+    region: process.env.AWS_REGION,
     accessKeyId: process.env.AWS_ACCESSKEYID,
     secretAccessKey: process.env.AWS_SECRETACCESSKEY,
   });
diff --git a/book/8-end/api/server/models/Discussion.ts b/book/8-end/api/server/models/Discussion.ts
index 850fd152..8160be46 100644
--- a/book/8-end/api/server/models/Discussion.ts
+++ b/book/8-end/api/server/models/Discussion.ts
@@ -24,7 +24,11 @@ const mongoSchema = new mongoose.Schema({
     type: String,
     required: true,
   },
-  memberIds: [String],
+  memberIds: [
+    {
+      type: String,
+    },
+  ],
   createdAt: {
     type: Date,
     required: true,
@@ -93,7 +97,7 @@ class DiscussionClass extends mongoose.Model {
 
     const filter: any = { teamId, memberIds: userId };
 
-    const discussions: any[] = await this.find(filter).lean();
+    const discussions: any[] = await this.find(filter).setOptions({ lean: true });
 
     return { discussions };
   }
@@ -122,7 +126,7 @@ class DiscussionClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const discussion = await this.findById(id).select('teamId createdUserId').lean();
+    const discussion = await this.findById(id).select('teamId createdUserId').setOptions({ lean: true });
 
     const team = await this.checkPermissionAndGetTeam({
       userId,
@@ -151,7 +155,7 @@ class DiscussionClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const discussion = await this.findById(id).select('teamId').lean();
+    const discussion = await this.findById(id).select('teamId').setOptions({ lean: true });
 
     await this.checkPermissionAndGetTeam({ userId, teamId: discussion.teamId });
 
@@ -167,7 +171,7 @@ class DiscussionClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const team = await Team.findById(teamId).select('memberIds teamLeaderId').lean();
+    const team = await Team.findById(teamId).select('memberIds teamLeaderId').setOptions({ lean: true });
 
     if (!team || team.memberIds.indexOf(userId) === -1) {
       throw new Error('Team not found');
diff --git a/book/8-end/api/server/models/EmailTemplate.ts b/book/8-end/api/server/models/EmailTemplate.ts
index fb8ae2e6..44cb9648 100644
--- a/book/8-end/api/server/models/EmailTemplate.ts
+++ b/book/8-end/api/server/models/EmailTemplate.ts
@@ -74,7 +74,7 @@ export async function insertTemplates() {
   ];
 
   for (const t of templates) {
-    const et = await EmailTemplate.findOne({ name: t.name }).lean();
+    const et = await EmailTemplate.findOne({ name: t.name }).setOptions({ lean: true });
     const message = t.message.replace(/\n/g, '').replace(/[ ]+/g, ' ').trim();
 
     if (!et) {
@@ -88,7 +88,7 @@ export async function insertTemplates() {
 export default async function getEmailTemplate(name: string, params: any) {
   await insertTemplates();
 
-  const et = await EmailTemplate.findOne({ name }).lean();
+  const et = await EmailTemplate.findOne({ name }).setOptions({ lean: true });
 
   if (!et) {
     throw new Error('Email Template is not found in database.');
diff --git a/book/8-end/api/server/models/Invitation.ts b/book/8-end/api/server/models/Invitation.ts
index c1d15471..60cd8dcf 100644
--- a/book/8-end/api/server/models/Invitation.ts
+++ b/book/8-end/api/server/models/Invitation.ts
@@ -68,12 +68,12 @@ class InvitationClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const team = await Team.findById(teamId).lean();
+    const team = await Team.findById(teamId).setOptions({ lean: true });
     if (!team || team.teamLeaderId !== userId) {
       throw new Error('Team does not exist or you have no permission');
     }
 
-    const registeredUser = await User.findOne({ email }).select('defaultTeamSlug').lean();
+    const registeredUser = await User.findOne({ email }).select('defaultTeamSlug').setOptions({ lean: true });
 
     if (registeredUser) {
       if (team.memberIds.includes(registeredUser._id.toString())) {
@@ -90,7 +90,7 @@ class InvitationClass extends mongoose.Model {
     }
 
     let token;
-    const invitation = await this.findOne({ teamId, email }).select('token').lean();
+    const invitation = await this.findOne({ teamId, email }).select('token').setOptions({ lean: true });
 
     if (invitation) {
       token = invitation.token;
@@ -125,17 +125,17 @@ class InvitationClass extends mongoose.Model {
       console.log('Email sending error:', err);
     });
 
-    return await this.findOne({ teamId, email }).lean();
+    return await this.findOne({ teamId, email }).setOptions({ lean: true });
   }
 
   public static async getTeamInvitations({ userId, teamId }) {
-    const team = await Team.findOne({ _id: teamId }).select('teamLeaderId').lean();
+    const team = await Team.findOne({ _id: teamId }).select('teamLeaderId').setOptions({ lean: true });
 
     if (userId !== team.teamLeaderId) {
       throw new Error('You have no permission.');
     }
 
-    return this.find({ teamId }).select('email').lean();
+    return this.find({ teamId }).select('email').setOptions({ lean: true });
   }
 
   public static async getTeamByToken({ token }) {
@@ -143,7 +143,7 @@ class InvitationClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const invitation = await this.findOne({ token }).lean();
+    const invitation = await this.findOne({ token }).setOptions({ lean: true });
 
     if (!invitation) {
       throw new Error('Invitation not found');
@@ -151,7 +151,7 @@ class InvitationClass extends mongoose.Model {
 
     const team = await Team.findById(invitation.teamId)
       .select('name slug avatarUrl memberIds')
-      .lean();
+      .setOptions({ lean: true });
 
     if (!team) {
       throw new Error('Team does not exist');
@@ -165,7 +165,7 @@ class InvitationClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const invitation = await this.findOne({ token }).lean();
+    const invitation = await this.findOne({ token }).setOptions({ lean: true });
 
     if (!invitation) {
       throw new Error('Invitation not found');
@@ -173,7 +173,7 @@ class InvitationClass extends mongoose.Model {
 
     const team = await Team.findById(invitation.teamId)
       .select('name slug avatarUrl memberIds')
-      .lean();
+      .setOptions({ lean: true });
 
     if (!team) {
       throw new Error('Team does not exist');
@@ -189,7 +189,7 @@ class InvitationClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const invitation = await this.findOne({ token }).lean();
+    const invitation = await this.findOne({ token }).setOptions({ lean: true });
 
     if (!invitation || invitation.email !== user.email) {
       throw new Error('Invitation not found');
@@ -199,7 +199,7 @@ class InvitationClass extends mongoose.Model {
 
     const team = await Team.findById(invitation.teamId)
       .select('memberIds slug teamLeaderId')
-      .lean();
+      .setOptions({ lean: true });
 
     if (!team) {
       throw new Error('Team does not exist');
diff --git a/book/8-end/api/server/models/Post.ts b/book/8-end/api/server/models/Post.ts
index ec47eab1..44e695e4 100644
--- a/book/8-end/api/server/models/Post.ts
+++ b/book/8-end/api/server/models/Post.ts
@@ -126,7 +126,7 @@ class PostClass extends mongoose.Model {
 
     const filter: any = { discussionId };
 
-    const posts: any[] = await this.find(filter).sort({ createdAt: 1 }).lean();
+    const posts: any[] = await this.find(filter).sort({ createdAt: 1 }).setOptions({ lean: true });
 
     return posts;
   }
@@ -156,7 +156,7 @@ class PostClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const post = await this.findById(id).select('createdUserId discussionId').lean();
+    const post = await this.findById(id).select('createdUserId discussionId').setOptions({ lean: true });
 
     await this.checkPermissionAndGetTeamAndDiscussion({
       userId,
@@ -180,7 +180,7 @@ class PostClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const post = await this.findById(id).select('createdUserId discussionId content').lean();
+    const post = await this.findById(id).select('createdUserId discussionId content').setOptions({ lean: true });
 
     await this.checkPermissionAndGetTeamAndDiscussion({
       userId,
@@ -206,7 +206,7 @@ class PostClass extends mongoose.Model {
 
     const discussion = await Discussion.findById(discussionId)
       .select('teamId memberIds slug')
-      .lean();
+      .setOptions({ lean: true });
 
     if (!discussion) {
       throw new Error('Discussion not found');
@@ -216,7 +216,7 @@ class PostClass extends mongoose.Model {
       throw new Error('Permission denied');
     }
 
-    const team = await Team.findById(discussion.teamId).select('memberIds slug').lean();
+    const team = await Team.findById(discussion.teamId).select('memberIds slug').setOptions({ lean: true });
 
     if (!team || team.memberIds.indexOf(userId) === -1) {
       throw new Error('Team not found');
diff --git a/book/8-end/api/server/models/Team.ts b/book/8-end/api/server/models/Team.ts
index f26f9e7f..37697b26 100644
--- a/book/8-end/api/server/models/Team.ts
+++ b/book/8-end/api/server/models/Team.ts
@@ -24,10 +24,12 @@ const mongoSchema = new mongoose.Schema({
     type: String,
     required: true,
   },
-  memberIds: {
-    type: [String],
-    required: true,
-  },
+  memberIds: [
+    {
+      type: String,
+      required: true,
+    },
+  ],
   defaultTeam: {
     type: Boolean,
     default: false,
@@ -128,12 +130,12 @@ class TeamClass extends mongoose.Model {
 
     await this.updateOne({ _id: teamId }, { $set: modifier }, { runValidators: true });
 
-    return this.findById(teamId, 'name avatarUrl slug defaultTeam').lean();
+    return this.findById(teamId, 'name avatarUrl slug defaultTeam').setOptions({ lean: true });
   }
 
   public static getAllTeamsForUser(userId: string) {
     console.log(`userId:${userId}`);
-    return this.find({ memberIds: userId }).lean();
+    return this.find({ memberIds: userId }).setOptions({ lean: true });
   }
 
   public static async removeMember({ teamId, teamLeaderId, userId }) {
diff --git a/book/8-end/api/server/models/User.ts b/book/8-end/api/server/models/User.ts
index c0415b1f..4fe818b0 100644
--- a/book/8-end/api/server/models/User.ts
+++ b/book/8-end/api/server/models/User.ts
@@ -120,7 +120,7 @@ class UserClass extends mongoose.Model {
   public static async getUserBySlug({ slug }) {
     console.log('Static method: getUserBySlug');
 
-    return this.findOne({ slug }, 'email displayName avatarUrl').lean();
+    return this.findOne({ slug }, 'email displayName avatarUrl').setOptions({ lean: true });
   }
 
   public static async updateProfile({ userId, name, avatarUrl }) {
@@ -139,7 +139,7 @@ class UserClass extends mongoose.Model {
 
     return this.findByIdAndUpdate(userId, { $set: modifier }, { new: true, runValidators: true })
       .select('displayName avatarUrl slug')
-      .lean();
+      .setOptions({ lean: true });
   }
 
   public static publicFields(): string[] {
@@ -165,7 +165,7 @@ class UserClass extends mongoose.Model {
   }) {
     const user = await this.findOne({ email })
       .select([...this.publicFields(), 'googleId'].join(' '))
-      .lean();
+      .setOptions({ lean: true });
 
     if (user) {
       if (_.isEmpty(googleToken) && user.googleId) {
@@ -227,7 +227,7 @@ class UserClass extends mongoose.Model {
   }
 
   public static async signInOrSignUpByPasswordless({ uid, email }) {
-    const user = await this.findOne({ email }).select(this.publicFields().join(' ')).lean();
+    const user = await this.findOne({ email }).select(this.publicFields().join(' ')).setOptions({ lean: true });
 
     if (user) {
       throw Error('User already exists');
@@ -278,7 +278,7 @@ class UserClass extends mongoose.Model {
 
     return this.find({ _id: { $in: team.memberIds } })
       .select(this.publicFields().join(' '))
-      .lean();
+      .setOptions({ lean: true });
   }
 
   private static async checkPermissionAndGetTeam({ userId, teamId }) {
@@ -288,7 +288,7 @@ class UserClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const team = await Team.findById(teamId).select('memberIds').lean();
+    const team = await Team.findById(teamId).select('memberIds').setOptions({ lean: true });
 
     if (!team || team.memberIds.indexOf(userId) === -1) {
       throw new Error('Team not found');
diff --git a/book/8-end/api/server/passwordless-auth.ts b/book/8-end/api/server/passwordless-auth.ts
index 3b3292b4..ac354223 100644
--- a/book/8-end/api/server/passwordless-auth.ts
+++ b/book/8-end/api/server/passwordless-auth.ts
@@ -50,7 +50,7 @@ function setupPasswordless({ server }) {
     '/auth/email-login-link',
     passwordless.requestToken(async (email, __, callback) => {
       try {
-        const user = await User.findOne({ email }).select('_id').lean();
+        const user = await User.findOne({ email }).select('_id').setOptions({ lean: true });
 
         if (user) {
           callback(null, user._id);
diff --git a/book/8-end/api/server/passwordless-token-mongostore.ts b/book/8-end/api/server/passwordless-token-mongostore.ts
index 55166cba..d6546e36 100644
--- a/book/8-end/api/server/passwordless-token-mongostore.ts
+++ b/book/8-end/api/server/passwordless-token-mongostore.ts
@@ -130,7 +130,7 @@ MongoStore.prototype.storeOrUpdateByEmail = async function addEmail(email: strin
     throw new Error('TokenStore:addEmail called with invalid parameters');
   }
 
-  const obj = await PasswordlessToken.findOne({ email }).select('uid').lean();
+  const obj = await PasswordlessToken.findOne({ email }).select('uid').setOptions({ lean: true });
 
   if (obj) {
     return obj.uid;
diff --git a/book/8-end/api/server/utils/slugify.ts b/book/8-end/api/server/utils/slugify.ts
index e76af3c6..f2394edd 100644
--- a/book/8-end/api/server/utils/slugify.ts
+++ b/book/8-end/api/server/utils/slugify.ts
@@ -5,7 +5,7 @@ const slugify = (text) => _.kebabCase(text);
 async function createUniqueSlug(Model, slug, count, filter) {
   const obj = await Model.findOne({ slug: `${slug}-${count}`, ...filter })
     .select('_id')
-    .lean();
+    .setOptions({ lean: true });
 
   if (!obj) {
     return `${slug}-${count}`;
@@ -19,7 +19,7 @@ async function generateSlug(Model, name, filter = {}) {
 
   const obj = await Model.findOne({ slug: origSlug, ...filter })
     .select('_id')
-    .lean();
+    .setOptions({ lean: true });
 
   if (!obj) {
     return origSlug;
@@ -31,7 +31,7 @@ async function generateSlug(Model, name, filter = {}) {
 async function generateNumberSlug(Model, filter = {}, n = 1) {
   const obj = await Model.findOne({ slug: n, ...filter })
     .select('_id')
-    .lean();
+    .setOptions({ lean: true });
 
   if (!obj) {
     return `${n}`;
diff --git a/book/9-begin/api/server/aws-s3.ts b/book/9-begin/api/server/aws-s3.ts
index 6d50475b..bf432d48 100644
--- a/book/9-begin/api/server/aws-s3.ts
+++ b/book/9-begin/api/server/aws-s3.ts
@@ -21,7 +21,7 @@ async function signRequestForUpload({ fileName, fileType, prefix, bucket }) {
 
   const s3 = new aws.S3({
     apiVersion: 'latest',
-    region: 'us-east-1',
+    region: process.env.AWS_REGION,
     accessKeyId: process.env.AWS_ACCESSKEYID,
     secretAccessKey: process.env.AWS_SECRETACCESSKEY,
   });
diff --git a/book/9-begin/api/server/aws-ses.ts b/book/9-begin/api/server/aws-ses.ts
index faf399eb..fff1565e 100644
--- a/book/9-begin/api/server/aws-ses.ts
+++ b/book/9-begin/api/server/aws-ses.ts
@@ -3,7 +3,7 @@ import * as aws from 'aws-sdk';
 export default function sendEmail(options) {
   const ses = new aws.SES({
     apiVersion: 'latest',
-    region: 'us-east-1',
+    region: process.env.AWS_REGION,
     accessKeyId: process.env.AWS_ACCESSKEYID,
     secretAccessKey: process.env.AWS_SECRETACCESSKEY,
   });
diff --git a/book/9-begin/api/server/models/Discussion.ts b/book/9-begin/api/server/models/Discussion.ts
index 850fd152..8160be46 100644
--- a/book/9-begin/api/server/models/Discussion.ts
+++ b/book/9-begin/api/server/models/Discussion.ts
@@ -24,7 +24,11 @@ const mongoSchema = new mongoose.Schema({
     type: String,
     required: true,
   },
-  memberIds: [String],
+  memberIds: [
+    {
+      type: String,
+    },
+  ],
   createdAt: {
     type: Date,
     required: true,
@@ -93,7 +97,7 @@ class DiscussionClass extends mongoose.Model {
 
     const filter: any = { teamId, memberIds: userId };
 
-    const discussions: any[] = await this.find(filter).lean();
+    const discussions: any[] = await this.find(filter).setOptions({ lean: true });
 
     return { discussions };
   }
@@ -122,7 +126,7 @@ class DiscussionClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const discussion = await this.findById(id).select('teamId createdUserId').lean();
+    const discussion = await this.findById(id).select('teamId createdUserId').setOptions({ lean: true });
 
     const team = await this.checkPermissionAndGetTeam({
       userId,
@@ -151,7 +155,7 @@ class DiscussionClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const discussion = await this.findById(id).select('teamId').lean();
+    const discussion = await this.findById(id).select('teamId').setOptions({ lean: true });
 
     await this.checkPermissionAndGetTeam({ userId, teamId: discussion.teamId });
 
@@ -167,7 +171,7 @@ class DiscussionClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const team = await Team.findById(teamId).select('memberIds teamLeaderId').lean();
+    const team = await Team.findById(teamId).select('memberIds teamLeaderId').setOptions({ lean: true });
 
     if (!team || team.memberIds.indexOf(userId) === -1) {
       throw new Error('Team not found');
diff --git a/book/9-begin/api/server/models/EmailTemplate.ts b/book/9-begin/api/server/models/EmailTemplate.ts
index fb8ae2e6..44cb9648 100644
--- a/book/9-begin/api/server/models/EmailTemplate.ts
+++ b/book/9-begin/api/server/models/EmailTemplate.ts
@@ -74,7 +74,7 @@ export async function insertTemplates() {
   ];
 
   for (const t of templates) {
-    const et = await EmailTemplate.findOne({ name: t.name }).lean();
+    const et = await EmailTemplate.findOne({ name: t.name }).setOptions({ lean: true });
     const message = t.message.replace(/\n/g, '').replace(/[ ]+/g, ' ').trim();
 
     if (!et) {
@@ -88,7 +88,7 @@ export async function insertTemplates() {
 export default async function getEmailTemplate(name: string, params: any) {
   await insertTemplates();
 
-  const et = await EmailTemplate.findOne({ name }).lean();
+  const et = await EmailTemplate.findOne({ name }).setOptions({ lean: true });
 
   if (!et) {
     throw new Error('Email Template is not found in database.');
diff --git a/book/9-begin/api/server/models/Invitation.ts b/book/9-begin/api/server/models/Invitation.ts
index c1d15471..60cd8dcf 100644
--- a/book/9-begin/api/server/models/Invitation.ts
+++ b/book/9-begin/api/server/models/Invitation.ts
@@ -68,12 +68,12 @@ class InvitationClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const team = await Team.findById(teamId).lean();
+    const team = await Team.findById(teamId).setOptions({ lean: true });
     if (!team || team.teamLeaderId !== userId) {
       throw new Error('Team does not exist or you have no permission');
     }
 
-    const registeredUser = await User.findOne({ email }).select('defaultTeamSlug').lean();
+    const registeredUser = await User.findOne({ email }).select('defaultTeamSlug').setOptions({ lean: true });
 
     if (registeredUser) {
       if (team.memberIds.includes(registeredUser._id.toString())) {
@@ -90,7 +90,7 @@ class InvitationClass extends mongoose.Model {
     }
 
     let token;
-    const invitation = await this.findOne({ teamId, email }).select('token').lean();
+    const invitation = await this.findOne({ teamId, email }).select('token').setOptions({ lean: true });
 
     if (invitation) {
       token = invitation.token;
@@ -125,17 +125,17 @@ class InvitationClass extends mongoose.Model {
       console.log('Email sending error:', err);
     });
 
-    return await this.findOne({ teamId, email }).lean();
+    return await this.findOne({ teamId, email }).setOptions({ lean: true });
   }
 
   public static async getTeamInvitations({ userId, teamId }) {
-    const team = await Team.findOne({ _id: teamId }).select('teamLeaderId').lean();
+    const team = await Team.findOne({ _id: teamId }).select('teamLeaderId').setOptions({ lean: true });
 
     if (userId !== team.teamLeaderId) {
       throw new Error('You have no permission.');
     }
 
-    return this.find({ teamId }).select('email').lean();
+    return this.find({ teamId }).select('email').setOptions({ lean: true });
   }
 
   public static async getTeamByToken({ token }) {
@@ -143,7 +143,7 @@ class InvitationClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const invitation = await this.findOne({ token }).lean();
+    const invitation = await this.findOne({ token }).setOptions({ lean: true });
 
     if (!invitation) {
       throw new Error('Invitation not found');
@@ -151,7 +151,7 @@ class InvitationClass extends mongoose.Model {
 
     const team = await Team.findById(invitation.teamId)
       .select('name slug avatarUrl memberIds')
-      .lean();
+      .setOptions({ lean: true });
 
     if (!team) {
       throw new Error('Team does not exist');
@@ -165,7 +165,7 @@ class InvitationClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const invitation = await this.findOne({ token }).lean();
+    const invitation = await this.findOne({ token }).setOptions({ lean: true });
 
     if (!invitation) {
       throw new Error('Invitation not found');
@@ -173,7 +173,7 @@ class InvitationClass extends mongoose.Model {
 
     const team = await Team.findById(invitation.teamId)
       .select('name slug avatarUrl memberIds')
-      .lean();
+      .setOptions({ lean: true });
 
     if (!team) {
       throw new Error('Team does not exist');
@@ -189,7 +189,7 @@ class InvitationClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const invitation = await this.findOne({ token }).lean();
+    const invitation = await this.findOne({ token }).setOptions({ lean: true });
 
     if (!invitation || invitation.email !== user.email) {
       throw new Error('Invitation not found');
@@ -199,7 +199,7 @@ class InvitationClass extends mongoose.Model {
 
     const team = await Team.findById(invitation.teamId)
       .select('memberIds slug teamLeaderId')
-      .lean();
+      .setOptions({ lean: true });
 
     if (!team) {
       throw new Error('Team does not exist');
diff --git a/book/9-begin/api/server/models/Post.ts b/book/9-begin/api/server/models/Post.ts
index ec47eab1..44e695e4 100644
--- a/book/9-begin/api/server/models/Post.ts
+++ b/book/9-begin/api/server/models/Post.ts
@@ -126,7 +126,7 @@ class PostClass extends mongoose.Model {
 
     const filter: any = { discussionId };
 
-    const posts: any[] = await this.find(filter).sort({ createdAt: 1 }).lean();
+    const posts: any[] = await this.find(filter).sort({ createdAt: 1 }).setOptions({ lean: true });
 
     return posts;
   }
@@ -156,7 +156,7 @@ class PostClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const post = await this.findById(id).select('createdUserId discussionId').lean();
+    const post = await this.findById(id).select('createdUserId discussionId').setOptions({ lean: true });
 
     await this.checkPermissionAndGetTeamAndDiscussion({
       userId,
@@ -180,7 +180,7 @@ class PostClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const post = await this.findById(id).select('createdUserId discussionId content').lean();
+    const post = await this.findById(id).select('createdUserId discussionId content').setOptions({ lean: true });
 
     await this.checkPermissionAndGetTeamAndDiscussion({
       userId,
@@ -206,7 +206,7 @@ class PostClass extends mongoose.Model {
 
     const discussion = await Discussion.findById(discussionId)
       .select('teamId memberIds slug')
-      .lean();
+      .setOptions({ lean: true });
 
     if (!discussion) {
       throw new Error('Discussion not found');
@@ -216,7 +216,7 @@ class PostClass extends mongoose.Model {
       throw new Error('Permission denied');
     }
 
-    const team = await Team.findById(discussion.teamId).select('memberIds slug').lean();
+    const team = await Team.findById(discussion.teamId).select('memberIds slug').setOptions({ lean: true });
 
     if (!team || team.memberIds.indexOf(userId) === -1) {
       throw new Error('Team not found');
diff --git a/book/9-begin/api/server/models/Team.ts b/book/9-begin/api/server/models/Team.ts
index f26f9e7f..37697b26 100644
--- a/book/9-begin/api/server/models/Team.ts
+++ b/book/9-begin/api/server/models/Team.ts
@@ -24,10 +24,12 @@ const mongoSchema = new mongoose.Schema({
     type: String,
     required: true,
   },
-  memberIds: {
-    type: [String],
-    required: true,
-  },
+  memberIds: [
+    {
+      type: String,
+      required: true,
+    },
+  ],
   defaultTeam: {
     type: Boolean,
     default: false,
@@ -128,12 +130,12 @@ class TeamClass extends mongoose.Model {
 
     await this.updateOne({ _id: teamId }, { $set: modifier }, { runValidators: true });
 
-    return this.findById(teamId, 'name avatarUrl slug defaultTeam').lean();
+    return this.findById(teamId, 'name avatarUrl slug defaultTeam').setOptions({ lean: true });
   }
 
   public static getAllTeamsForUser(userId: string) {
     console.log(`userId:${userId}`);
-    return this.find({ memberIds: userId }).lean();
+    return this.find({ memberIds: userId }).setOptions({ lean: true });
   }
 
   public static async removeMember({ teamId, teamLeaderId, userId }) {
diff --git a/book/9-begin/api/server/models/User.ts b/book/9-begin/api/server/models/User.ts
index c0415b1f..4fe818b0 100644
--- a/book/9-begin/api/server/models/User.ts
+++ b/book/9-begin/api/server/models/User.ts
@@ -120,7 +120,7 @@ class UserClass extends mongoose.Model {
   public static async getUserBySlug({ slug }) {
     console.log('Static method: getUserBySlug');
 
-    return this.findOne({ slug }, 'email displayName avatarUrl').lean();
+    return this.findOne({ slug }, 'email displayName avatarUrl').setOptions({ lean: true });
   }
 
   public static async updateProfile({ userId, name, avatarUrl }) {
@@ -139,7 +139,7 @@ class UserClass extends mongoose.Model {
 
     return this.findByIdAndUpdate(userId, { $set: modifier }, { new: true, runValidators: true })
       .select('displayName avatarUrl slug')
-      .lean();
+      .setOptions({ lean: true });
   }
 
   public static publicFields(): string[] {
@@ -165,7 +165,7 @@ class UserClass extends mongoose.Model {
   }) {
     const user = await this.findOne({ email })
       .select([...this.publicFields(), 'googleId'].join(' '))
-      .lean();
+      .setOptions({ lean: true });
 
     if (user) {
       if (_.isEmpty(googleToken) && user.googleId) {
@@ -227,7 +227,7 @@ class UserClass extends mongoose.Model {
   }
 
   public static async signInOrSignUpByPasswordless({ uid, email }) {
-    const user = await this.findOne({ email }).select(this.publicFields().join(' ')).lean();
+    const user = await this.findOne({ email }).select(this.publicFields().join(' ')).setOptions({ lean: true });
 
     if (user) {
       throw Error('User already exists');
@@ -278,7 +278,7 @@ class UserClass extends mongoose.Model {
 
     return this.find({ _id: { $in: team.memberIds } })
       .select(this.publicFields().join(' '))
-      .lean();
+      .setOptions({ lean: true });
   }
 
   private static async checkPermissionAndGetTeam({ userId, teamId }) {
@@ -288,7 +288,7 @@ class UserClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const team = await Team.findById(teamId).select('memberIds').lean();
+    const team = await Team.findById(teamId).select('memberIds').setOptions({ lean: true });
 
     if (!team || team.memberIds.indexOf(userId) === -1) {
       throw new Error('Team not found');
diff --git a/book/9-begin/api/server/passwordless-auth.ts b/book/9-begin/api/server/passwordless-auth.ts
index 3b3292b4..ac354223 100644
--- a/book/9-begin/api/server/passwordless-auth.ts
+++ b/book/9-begin/api/server/passwordless-auth.ts
@@ -50,7 +50,7 @@ function setupPasswordless({ server }) {
     '/auth/email-login-link',
     passwordless.requestToken(async (email, __, callback) => {
       try {
-        const user = await User.findOne({ email }).select('_id').lean();
+        const user = await User.findOne({ email }).select('_id').setOptions({ lean: true });
 
         if (user) {
           callback(null, user._id);
diff --git a/book/9-begin/api/server/passwordless-token-mongostore.ts b/book/9-begin/api/server/passwordless-token-mongostore.ts
index 55166cba..d6546e36 100644
--- a/book/9-begin/api/server/passwordless-token-mongostore.ts
+++ b/book/9-begin/api/server/passwordless-token-mongostore.ts
@@ -130,7 +130,7 @@ MongoStore.prototype.storeOrUpdateByEmail = async function addEmail(email: strin
     throw new Error('TokenStore:addEmail called with invalid parameters');
   }
 
-  const obj = await PasswordlessToken.findOne({ email }).select('uid').lean();
+  const obj = await PasswordlessToken.findOne({ email }).select('uid').setOptions({ lean: true });
 
   if (obj) {
     return obj.uid;
diff --git a/book/9-begin/api/server/utils/slugify.ts b/book/9-begin/api/server/utils/slugify.ts
index e76af3c6..f2394edd 100644
--- a/book/9-begin/api/server/utils/slugify.ts
+++ b/book/9-begin/api/server/utils/slugify.ts
@@ -5,7 +5,7 @@ const slugify = (text) => _.kebabCase(text);
 async function createUniqueSlug(Model, slug, count, filter) {
   const obj = await Model.findOne({ slug: `${slug}-${count}`, ...filter })
     .select('_id')
-    .lean();
+    .setOptions({ lean: true });
 
   if (!obj) {
     return `${slug}-${count}`;
@@ -19,7 +19,7 @@ async function generateSlug(Model, name, filter = {}) {
 
   const obj = await Model.findOne({ slug: origSlug, ...filter })
     .select('_id')
-    .lean();
+    .setOptions({ lean: true });
 
   if (!obj) {
     return origSlug;
@@ -31,7 +31,7 @@ async function generateSlug(Model, name, filter = {}) {
 async function generateNumberSlug(Model, filter = {}, n = 1) {
   const obj = await Model.findOne({ slug: n, ...filter })
     .select('_id')
-    .lean();
+    .setOptions({ lean: true });
 
   if (!obj) {
     return `${n}`;
diff --git a/book/9-end/api/server/api/team-leader.ts b/book/9-end/api/server/api/team-leader.ts
index db9eecc5..fbfb0082 100644
--- a/book/9-end/api/server/api/team-leader.ts
+++ b/book/9-end/api/server/api/team-leader.ts
@@ -93,11 +93,13 @@ router.post('/stripe/fetch-checkout-session', async (req, res, next) => {
   try {
     const { mode, teamId } = req.body;
 
-    const user = await User.findById(req.user.id).select(['stripeCustomer', 'email']).lean();
+    const user = await User.findById(req.user.id)
+      .select(['stripeCustomer', 'email'])
+      .setOptions({ lean: true });
 
     const team = await Team.findById(teamId)
       .select(['stripeSubscription', 'slug', 'teamLeaderId'])
-      .lean();
+      .setOptions({ lean: true });
 
     if (!user || !team || team.teamLeaderId !== req.user.id) {
       throw new Error('Permission denied');
diff --git a/book/9-end/api/server/aws-s3.ts b/book/9-end/api/server/aws-s3.ts
index 6d50475b..bf432d48 100644
--- a/book/9-end/api/server/aws-s3.ts
+++ b/book/9-end/api/server/aws-s3.ts
@@ -21,7 +21,7 @@ async function signRequestForUpload({ fileName, fileType, prefix, bucket }) {
 
   const s3 = new aws.S3({
     apiVersion: 'latest',
-    region: 'us-east-1',
+    region: process.env.AWS_REGION,
     accessKeyId: process.env.AWS_ACCESSKEYID,
     secretAccessKey: process.env.AWS_SECRETACCESSKEY,
   });
diff --git a/book/9-end/api/server/aws-ses.ts b/book/9-end/api/server/aws-ses.ts
index faf399eb..fff1565e 100644
--- a/book/9-end/api/server/aws-ses.ts
+++ b/book/9-end/api/server/aws-ses.ts
@@ -3,7 +3,7 @@ import * as aws from 'aws-sdk';
 export default function sendEmail(options) {
   const ses = new aws.SES({
     apiVersion: 'latest',
-    region: 'us-east-1',
+    region: process.env.AWS_REGION,
     accessKeyId: process.env.AWS_ACCESSKEYID,
     secretAccessKey: process.env.AWS_SECRETACCESSKEY,
   });
diff --git a/book/9-end/api/server/models/Discussion.ts b/book/9-end/api/server/models/Discussion.ts
index e9931e9d..5b2c78e8 100644
--- a/book/9-end/api/server/models/Discussion.ts
+++ b/book/9-end/api/server/models/Discussion.ts
@@ -24,7 +24,11 @@ const mongoSchema = new mongoose.Schema({
     type: String,
     required: true,
   },
-  memberIds: [String],
+  memberIds: [
+    {
+      type: String,
+    },
+  ],
   createdAt: {
     type: Date,
     required: true,
@@ -104,7 +108,7 @@ class DiscussionClass extends mongoose.Model {
 
     const filter: any = { teamId, memberIds: userId };
 
-    const discussions: any[] = await this.find(filter).lean();
+    const discussions: any[] = await this.find(filter).setOptions({ lean: true });
 
     return { discussions };
   }
@@ -134,7 +138,9 @@ class DiscussionClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const discussion = await this.findById(id).select('teamId createdUserId').lean();
+    const discussion = await this.findById(id)
+      .select('teamId createdUserId')
+      .setOptions({ lean: true });
 
     const team = await this.checkPermissionAndGetTeam({
       userId,
@@ -164,7 +170,7 @@ class DiscussionClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const discussion = await this.findById(id).select('teamId').lean();
+    const discussion = await this.findById(id).select('teamId').setOptions({ lean: true });
 
     await this.checkPermissionAndGetTeam({ userId, teamId: discussion.teamId });
 
@@ -180,7 +186,9 @@ class DiscussionClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const team = await Team.findById(teamId).select('memberIds teamLeaderId').lean();
+    const team = await Team.findById(teamId)
+      .select('memberIds teamLeaderId')
+      .setOptions({ lean: true });
 
     if (!team || team.memberIds.indexOf(userId) === -1) {
       throw new Error('Team not found');
diff --git a/book/9-end/api/server/models/EmailTemplate.ts b/book/9-end/api/server/models/EmailTemplate.ts
index 54ca2241..db9089d7 100644
--- a/book/9-end/api/server/models/EmailTemplate.ts
+++ b/book/9-end/api/server/models/EmailTemplate.ts
@@ -74,7 +74,7 @@ export async function insertTemplates() {
   ];
 
   for (const t of templates) {
-    const et = await EmailTemplate.findOne({ name: t.name }).lean();
+    const et = await EmailTemplate.findOne({ name: t.name }).setOptions({ lean: true });
     const message = t.message.replace(/\n/g, '').replace(/[ ]+/g, ' ').trim();
 
     if (!et) {
@@ -88,7 +88,7 @@ export async function insertTemplates() {
 export default async function getEmailTemplate(name: string, params: any) {
   await insertTemplates();
 
-  const et = await EmailTemplate.findOne({ name }).lean();
+  const et = await EmailTemplate.findOne({ name }).setOptions({ lean: true });
 
   if (!et) {
     throw new Error('Email Template is not found in database.');
diff --git a/book/9-end/api/server/models/Invitation.ts b/book/9-end/api/server/models/Invitation.ts
index c1d15471..60cd8dcf 100644
--- a/book/9-end/api/server/models/Invitation.ts
+++ b/book/9-end/api/server/models/Invitation.ts
@@ -68,12 +68,12 @@ class InvitationClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const team = await Team.findById(teamId).lean();
+    const team = await Team.findById(teamId).setOptions({ lean: true });
     if (!team || team.teamLeaderId !== userId) {
       throw new Error('Team does not exist or you have no permission');
     }
 
-    const registeredUser = await User.findOne({ email }).select('defaultTeamSlug').lean();
+    const registeredUser = await User.findOne({ email }).select('defaultTeamSlug').setOptions({ lean: true });
 
     if (registeredUser) {
       if (team.memberIds.includes(registeredUser._id.toString())) {
@@ -90,7 +90,7 @@ class InvitationClass extends mongoose.Model {
     }
 
     let token;
-    const invitation = await this.findOne({ teamId, email }).select('token').lean();
+    const invitation = await this.findOne({ teamId, email }).select('token').setOptions({ lean: true });
 
     if (invitation) {
       token = invitation.token;
@@ -125,17 +125,17 @@ class InvitationClass extends mongoose.Model {
       console.log('Email sending error:', err);
     });
 
-    return await this.findOne({ teamId, email }).lean();
+    return await this.findOne({ teamId, email }).setOptions({ lean: true });
   }
 
   public static async getTeamInvitations({ userId, teamId }) {
-    const team = await Team.findOne({ _id: teamId }).select('teamLeaderId').lean();
+    const team = await Team.findOne({ _id: teamId }).select('teamLeaderId').setOptions({ lean: true });
 
     if (userId !== team.teamLeaderId) {
       throw new Error('You have no permission.');
     }
 
-    return this.find({ teamId }).select('email').lean();
+    return this.find({ teamId }).select('email').setOptions({ lean: true });
   }
 
   public static async getTeamByToken({ token }) {
@@ -143,7 +143,7 @@ class InvitationClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const invitation = await this.findOne({ token }).lean();
+    const invitation = await this.findOne({ token }).setOptions({ lean: true });
 
     if (!invitation) {
       throw new Error('Invitation not found');
@@ -151,7 +151,7 @@ class InvitationClass extends mongoose.Model {
 
     const team = await Team.findById(invitation.teamId)
       .select('name slug avatarUrl memberIds')
-      .lean();
+      .setOptions({ lean: true });
 
     if (!team) {
       throw new Error('Team does not exist');
@@ -165,7 +165,7 @@ class InvitationClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const invitation = await this.findOne({ token }).lean();
+    const invitation = await this.findOne({ token }).setOptions({ lean: true });
 
     if (!invitation) {
       throw new Error('Invitation not found');
@@ -173,7 +173,7 @@ class InvitationClass extends mongoose.Model {
 
     const team = await Team.findById(invitation.teamId)
       .select('name slug avatarUrl memberIds')
-      .lean();
+      .setOptions({ lean: true });
 
     if (!team) {
       throw new Error('Team does not exist');
@@ -189,7 +189,7 @@ class InvitationClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const invitation = await this.findOne({ token }).lean();
+    const invitation = await this.findOne({ token }).setOptions({ lean: true });
 
     if (!invitation || invitation.email !== user.email) {
       throw new Error('Invitation not found');
@@ -199,7 +199,7 @@ class InvitationClass extends mongoose.Model {
 
     const team = await Team.findById(invitation.teamId)
       .select('memberIds slug teamLeaderId')
-      .lean();
+      .setOptions({ lean: true });
 
     if (!team) {
       throw new Error('Team does not exist');
diff --git a/book/9-end/api/server/models/Post.ts b/book/9-end/api/server/models/Post.ts
index ec47eab1..e612a735 100644
--- a/book/9-end/api/server/models/Post.ts
+++ b/book/9-end/api/server/models/Post.ts
@@ -126,7 +126,7 @@ class PostClass extends mongoose.Model {
 
     const filter: any = { discussionId };
 
-    const posts: any[] = await this.find(filter).sort({ createdAt: 1 }).lean();
+    const posts: any[] = await this.find(filter).sort({ createdAt: 1 }).setOptions({ lean: true });
 
     return posts;
   }
@@ -156,7 +156,9 @@ class PostClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const post = await this.findById(id).select('createdUserId discussionId').lean();
+    const post = await this.findById(id)
+      .select('createdUserId discussionId')
+      .setOptions({ lean: true });
 
     await this.checkPermissionAndGetTeamAndDiscussion({
       userId,
@@ -180,7 +182,9 @@ class PostClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const post = await this.findById(id).select('createdUserId discussionId content').lean();
+    const post = await this.findById(id)
+      .select('createdUserId discussionId content')
+      .setOptions({ lean: true });
 
     await this.checkPermissionAndGetTeamAndDiscussion({
       userId,
@@ -206,7 +210,7 @@ class PostClass extends mongoose.Model {
 
     const discussion = await Discussion.findById(discussionId)
       .select('teamId memberIds slug')
-      .lean();
+      .setOptions({ lean: true });
 
     if (!discussion) {
       throw new Error('Discussion not found');
@@ -216,7 +220,9 @@ class PostClass extends mongoose.Model {
       throw new Error('Permission denied');
     }
 
-    const team = await Team.findById(discussion.teamId).select('memberIds slug').lean();
+    const team = await Team.findById(discussion.teamId)
+      .select('memberIds slug')
+      .setOptions({ lean: true });
 
     if (!team || team.memberIds.indexOf(userId) === -1) {
       throw new Error('Team not found');
diff --git a/book/9-end/api/server/models/Team.ts b/book/9-end/api/server/models/Team.ts
index 49a2eb2f..047cc105 100644
--- a/book/9-end/api/server/models/Team.ts
+++ b/book/9-end/api/server/models/Team.ts
@@ -26,10 +26,12 @@ const mongoSchema = new mongoose.Schema({
     type: String,
     required: true,
   },
-  memberIds: {
-    type: [String],
-    required: true,
-  },
+  memberIds: [
+    {
+      type: String,
+      required: true,
+    },
+  ],
   defaultTeam: {
     type: Boolean,
     default: false,
@@ -183,12 +185,12 @@ class TeamClass extends mongoose.Model {
 
     await this.updateOne({ _id: teamId }, { $set: modifier }, { runValidators: true });
 
-    return this.findById(teamId, 'name avatarUrl slug defaultTeam').lean();
+    return this.findById(teamId, 'name avatarUrl slug defaultTeam').setOptions({ lean: true });
   }
 
   public static getAllTeamsForUser(userId: string) {
     console.log(`userId:${userId}`);
-    return this.find({ memberIds: userId }).lean();
+    return this.find({ memberIds: userId }).setOptions({ lean: true });
   }
 
   public static async removeMember({ teamId, teamLeaderId, userId }) {
@@ -259,13 +261,13 @@ class TeamClass extends mongoose.Model {
       { new: true, runValidators: true },
     )
       .select('isSubscriptionActive stripeSubscription')
-      .lean();
+      .setOptions({ lean: true });
   }
 
   public static async cancelSubscriptionAfterFailedPayment({ subscriptionId }) {
     const team: any = await this.find({ 'stripeSubscription.id': subscriptionId })
       .select('teamLeaderId isSubscriptionActive stripeSubscription isPaymentFailed')
-      .lean();
+      .setOptions({ lean: true });
     if (!team.isSubscriptionActive) {
       throw new Error('Team is already unsubscribed.');
     }
@@ -285,7 +287,7 @@ class TeamClass extends mongoose.Model {
       { new: true, runValidators: true },
     )
       .select('isSubscriptionActive stripeSubscription isPaymentFailed')
-      .lean();
+      .setOptions({ lean: true });
   }
 }
 
diff --git a/book/9-end/api/server/models/User.ts b/book/9-end/api/server/models/User.ts
index 9dd1158d..9a91292a 100644
--- a/book/9-end/api/server/models/User.ts
+++ b/book/9-end/api/server/models/User.ts
@@ -221,7 +221,7 @@ class UserClass extends mongoose.Model {
   public static async getUserBySlug({ slug }) {
     console.log('Static method: getUserBySlug');
 
-    return this.findOne({ slug }, 'email displayName avatarUrl').lean();
+    return this.findOne({ slug }, 'email displayName avatarUrl').setOptions({ lean: true });
   }
 
   public static async updateProfile({ userId, name, avatarUrl }) {
@@ -240,7 +240,7 @@ class UserClass extends mongoose.Model {
 
     return this.findByIdAndUpdate(userId, { $set: modifier }, { new: true, runValidators: true })
       .select('displayName avatarUrl slug')
-      .lean();
+      .setOptions({ lean: true });
   }
 
   public static publicFields(): string[] {
@@ -269,7 +269,7 @@ class UserClass extends mongoose.Model {
   }) {
     const user = await this.findOne({ email })
       .select([...this.publicFields(), 'googleId'].join(' '))
-      .lean();
+      .setOptions({ lean: true });
 
     if (user) {
       if (_.isEmpty(googleToken) && user.googleId) {
@@ -331,7 +331,9 @@ class UserClass extends mongoose.Model {
   }
 
   public static async signInOrSignUpByPasswordless({ uid, email }) {
-    const user = await this.findOne({ email }).select(this.publicFields().join(' ')).lean();
+    const user = await this.findOne({ email })
+      .select(this.publicFields().join(' '))
+      .setOptions({ lean: true });
 
     if (user) {
       throw Error('User already exists');
@@ -382,7 +384,7 @@ class UserClass extends mongoose.Model {
 
     return this.find({ _id: { $in: team.memberIds } })
       .select(this.publicFields().join(' '))
-      .lean();
+      .setOptions({ lean: true });
   }
 
   public static async saveStripeCustomerAndCard({
@@ -456,7 +458,7 @@ class UserClass extends mongoose.Model {
 
     return this.findByIdAndUpdate(userId, { $set: modifier }, { new: true, runValidators: true })
       .select('stripeListOfInvoices')
-      .lean();
+      .setOptions({ lean: true });
   }
 
   private static async checkPermissionAndGetTeam({ userId, teamId }) {
@@ -466,7 +468,7 @@ class UserClass extends mongoose.Model {
       throw new Error('Bad data');
     }
 
-    const team = await Team.findById(teamId).select('memberIds').lean();
+    const team = await Team.findById(teamId).select('memberIds').setOptions({ lean: true });
 
     if (!team || team.memberIds.indexOf(userId) === -1) {
       throw new Error('Team not found');
diff --git a/book/9-end/api/server/passwordless-auth.ts b/book/9-end/api/server/passwordless-auth.ts
index 3b3292b4..ac354223 100644
--- a/book/9-end/api/server/passwordless-auth.ts
+++ b/book/9-end/api/server/passwordless-auth.ts
@@ -50,7 +50,7 @@ function setupPasswordless({ server }) {
     '/auth/email-login-link',
     passwordless.requestToken(async (email, __, callback) => {
       try {
-        const user = await User.findOne({ email }).select('_id').lean();
+        const user = await User.findOne({ email }).select('_id').setOptions({ lean: true });
 
         if (user) {
           callback(null, user._id);
diff --git a/book/9-end/api/server/passwordless-token-mongostore.ts b/book/9-end/api/server/passwordless-token-mongostore.ts
index 55166cba..d6546e36 100644
--- a/book/9-end/api/server/passwordless-token-mongostore.ts
+++ b/book/9-end/api/server/passwordless-token-mongostore.ts
@@ -130,7 +130,7 @@ MongoStore.prototype.storeOrUpdateByEmail = async function addEmail(email: strin
     throw new Error('TokenStore:addEmail called with invalid parameters');
   }
 
-  const obj = await PasswordlessToken.findOne({ email }).select('uid').lean();
+  const obj = await PasswordlessToken.findOne({ email }).select('uid').setOptions({ lean: true });
 
   if (obj) {
     return obj.uid;
diff --git a/book/9-end/api/server/stripe.ts b/book/9-end/api/server/stripe.ts
index a0f0b116..90d7080d 100644
--- a/book/9-end/api/server/stripe.ts
+++ b/book/9-end/api/server/stripe.ts
@@ -121,12 +121,12 @@ function stripeWebhookAndCheckoutCallback({ server }) {
     const user = await User.findById(
       session.metadata.userId,
       '_id stripeCustomer email displayName isSubscriptionActive stripeSubscription',
-    ).lean();
+    ).setOptions({ lean: true });
 
     const team = await Team.findById(
       session.metadata.teamId,
       'isSubscriptionActive stripeSubscription teamLeaderId slug',
-    ).lean();
+    ).setOptions({ lean: true });
 
     if (!user) {
       throw new Error('User not found.');
diff --git a/book/9-end/api/server/utils/slugify.ts b/book/9-end/api/server/utils/slugify.ts
index e76af3c6..f2394edd 100644
--- a/book/9-end/api/server/utils/slugify.ts
+++ b/book/9-end/api/server/utils/slugify.ts
@@ -5,7 +5,7 @@ const slugify = (text) => _.kebabCase(text);
 async function createUniqueSlug(Model, slug, count, filter) {
   const obj = await Model.findOne({ slug: `${slug}-${count}`, ...filter })
     .select('_id')
-    .lean();
+    .setOptions({ lean: true });
 
   if (!obj) {
     return `${slug}-${count}`;
@@ -19,7 +19,7 @@ async function generateSlug(Model, name, filter = {}) {
 
   const obj = await Model.findOne({ slug: origSlug, ...filter })
     .select('_id')
-    .lean();
+    .setOptions({ lean: true });
 
   if (!obj) {
     return origSlug;
@@ -31,7 +31,7 @@ async function generateSlug(Model, name, filter = {}) {
 async function generateNumberSlug(Model, filter = {}, n = 1) {
   const obj = await Model.findOne({ slug: n, ...filter })
     .select('_id')
-    .lean();
+    .setOptions({ lean: true });
 
   if (!obj) {
     return `${n}`;
diff --git a/book/9-end/lambda/handler.ts b/book/9-end/lambda/handler.ts
index 43918a6c..26fa72d2 100644
--- a/book/9-end/lambda/handler.ts
+++ b/book/9-end/lambda/handler.ts
@@ -39,7 +39,7 @@ export const sendEmailForNewPost = async (event) => {
 
     const usersToNotify = await User.find({ _id: { $in: userIds } })
       .select('email')
-      .lean();
+      .setOptions({ lean: true });
 
     console.log('usersToNotify', usersToNotify);
 
diff --git a/saas/app/pages/team-settings.tsx b/saas/app/pages/team-settings.tsx
index e06a07cf..4010b1ab 100644
--- a/saas/app/pages/team-settings.tsx
+++ b/saas/app/pages/team-settings.tsx
@@ -221,7 +221,7 @@ class TeamSettings extends React.Component<Props, State> {
             <React.Fragment>
               <h4>Invited users</h4>
               <p />
-              <TableContainer component={Paper}>
+              <TableContainer>
                 <Table>
                   <TableHead>
                     <TableRow>