Refactor DB setup Part 1 (#105)

* Separate CreateStory DB operation to own function

Improves testability for unit testing.

* Add sample create DB test

* Separate DeleteStory DB operation to own function

* Separate CreateUser DB operation to own function

* Add TODO

* Separate DeleteUser DB operation to own function

* Fix pointer errors

model/stories.go

@@ -47,15 +47,20 @@ func GetStoryByID(db *gorm.DB, id int) (Story, error) {
 	return story, nil
 }
 
-func CreateStory(db *gorm.DB, story *Story) error {
-	err := db.
+func (s *Story) create(tx *gorm.DB) *gorm.DB {
+	return tx.
 		Preload(clause.Associations).
-		Create(story).
+		Create(s).
 		// Get associated Author. See
 		// https://github.com/go-gorm/gen/issues/618 on why
 		// a separate .First() is needed.
-		First(story).
-		Error
+		First(s)
+}
+
+func CreateStory(db *gorm.DB, story *Story) error {
+	err := db.Transaction(func(tx *gorm.DB) error {
+		return story.create(tx).Error
+	})
 	if err != nil {
 		return database.HandleDBError(err, "story")
 	}
@@ -109,14 +114,19 @@ func UpdateStory(db *gorm.DB, storyID int, newStory *Story) error {
 	return nil
 }
 
-func DeleteStory(db *gorm.DB, storyID int) (Story, error) {
-	var story Story
-	err := db.
+func (s *Story) delete(tx *gorm.DB, storyID uint) *gorm.DB {
+	return tx.
 		Preload(clause.Associations).
 		Where("id = ?", storyID).
-		First(&story). // store the value to be returned
-		Delete(&story).
-		Error
+		First(s). // store the value to be returned
+		Delete(s)
+}
+
+func DeleteStory(db *gorm.DB, storyID int) (Story, error) {
+	var story Story
+	err := db.Transaction(func(tx *gorm.DB) error {
+		return story.delete(tx, uint(storyID)).Error
+	})
 	if err != nil {
 		return story, database.HandleDBError(err, "story")
 	}

model/stories_test.go

@@ -9,6 +9,7 @@ import (
 	userenums "github.com/source-academy/stories-backend/internal/enums/users"
 	"github.com/source-academy/stories-backend/internal/testutils"
 	"github.com/stretchr/testify/assert"
+	"gorm.io/gorm"
 )
 
 // FIXME: Coupling with the other operations in the users database
@@ -40,6 +41,25 @@ var (
 	}
 )
 
+func TestCreate(t *testing.T) {
+	t.Run("", func(t *testing.T) {
+		db, cleanUp := testutils.SetupDBConnection(t, dbConfig, migrationPath)
+		defer cleanUp(t)
+
+		// Any number is fine because the statement is not executed,
+		// thus removing the coupling with an actual author having to be
+		// created prior.
+		story := &Story{
+			AuthorID: 1,
+			Content:  "The quick brown test content 5678.",
+		}
+		sql := db.ToSQL(func(tx *gorm.DB) *gorm.DB {
+			return story.create(tx)
+		})
+		assert.Contains(t, sql, "The quick brown test content 5678.", "Should contain the story content")
+	})
+}
+
 func TestCreateStory(t *testing.T) {
 	t.Run("should increase the total story count", func(t *testing.T) {
 		db, cleanUp := testutils.SetupDBConnection(t, dbConfig, migrationPath)
@@ -221,8 +241,8 @@ func TestStoryDB(t *testing.T) {
 		}
 		_ = CreateGroup(db, &group)
 
-		err := db.Exec(`INSERT INTO "stories" 
-		("created_at","updated_at","deleted_at","author_id","group_id","title","content","pin_order") 
+		err := db.Exec(`INSERT INTO "stories"
+		("created_at","updated_at","deleted_at","author_id","group_id","title","content","pin_order")
 		VALUES ('2023-08-08 22:17:28.085','2023-08-08 22:17:28.085',NULL,NULL,NULL,'','# Hi, This is a test story.',NULL)`).
 			Error
 		var pgerr *pgconn.PgError

model/users.go

@@ -31,16 +31,24 @@ func GetUserByID(db *gorm.DB, id int) (User, error) {
 	return user, err
 }
 
-func CreateUser(db *gorm.DB, user *User) error {
+func (u *User) create(tx *gorm.DB) *gorm.DB {
 	// TODO: If user already exists, but is soft-deleted, undelete the user
-	err := db.Create(user).Error
+	return tx.Create(u)
+}
+
+func CreateUser(db *gorm.DB, user *User) error {
+	err := db.Transaction(func(tx *gorm.DB) error {
+		return user.create(tx).Error
+	})
 	if err != nil {
 		return database.HandleDBError(err, "user")
 	}
 	return nil
 }
 
 func CreateUsers(db *gorm.DB, users *[]*User) (int64, error) {
+	// TODO: Use users.create() instead
+	// Blocked by `RowsAffected` not being accessible.
 	tx := db.Create(users)
 	rowCount := tx.RowsAffected
 	if err := tx.Error; err != nil {
@@ -49,14 +57,19 @@ func CreateUsers(db *gorm.DB, users *[]*User) (int64, error) {
 	return rowCount, nil
 }
 
+func (u *User) delete(tx *gorm.DB, userID uint) *gorm.DB {
+	return tx.
+		Model(u).
+		Where("id = ?", userID).
+		First(u). // store the value to be returned
+		Delete(u)
+}
+
 func DeleteUser(db *gorm.DB, userID int) (User, error) {
 	var user User
-	err := db.
-		Model(&user).
-		Where("id = ?", userID).
-		First(&user). // store the value to be returned
-		Delete(&user).
-		Error
+	err := db.Transaction(func(tx *gorm.DB) error {
+		return user.delete(tx, uint(userID)).Error
+	})
 	if err != nil {
 		return user, database.HandleDBError(err, "user")
 	}