test: add tests on lookup generator

packages/forest_admin_datasource_mongoid/lib/forest_admin_datasource_mongoid/utils/pipeline/lookup_generator.rb

@@ -26,6 +26,8 @@ def self.lookup_projection(current_path, schema_stack, projection, options)
             fields.merge!(add_fields(name, relation_projection, options))
           end
 
+          pipeline.push({ '$addFields' => fields }) unless fields.empty?
+
           pipeline
         end
 
@@ -36,7 +38,7 @@ def self.add_fields(name, projection, options)
           projection.filter { |field| field.include?('@@@') }
                     .map { |field_name| "#{name}.#{field_name.tr(":", ".")}" }
                     .each_with_object({}) do |curr, acc|
-                      acc[curr] = "$#{curr.tr("@@@", ".")}"
+                      acc[curr] = "$#{curr.gsub("@@@", ".")}"
                     end
         end
 
@@ -67,8 +69,10 @@ def self.lookup_relation(current_path, schema_stack, name, projection, options)
 
             return [
               # Push lookup to pipeline
-              { '$lookup' =>
-                { 'from' => from, 'localField' => local_field, 'foreignField' => foreign_field, 'as' => as } },
+              {
+                '$lookup' => { 'from' => from, 'localField' => local_field, 'foreignField' => foreign_field,
+                               'as' => as }
+              },
               { '$unwind' => { 'path' => "$#{as}", 'preserveNullAndEmptyArrays' => true } },
 
               # Recurse to get relations of relations

packages/forest_admin_datasource_mongoid/spec/dummy/app/models/address.rb

@@ -4,5 +4,6 @@ class Address
   field :city, type: String
   field :zip_code, type: String
 
+  embeds_one :meta, class_name: 'Meta'
   embedded_in :user
 end

packages/forest_admin_datasource_mongoid/spec/dummy/app/models/author.rb

@@ -5,4 +5,5 @@ class Author
   field :last_name, type: String
 
   belongs_to :post
+  belongs_to :user
 end

packages/forest_admin_datasource_mongoid/spec/dummy/app/models/co_author.rb

@@ -0,0 +1,8 @@
+class CoAuthor
+  include Mongoid::Document
+  include Mongoid::Timestamps
+  field :first_name, type: String
+  field :last_name, type: String
+
+  belongs_to :user
+end

packages/forest_admin_datasource_mongoid/spec/dummy/app/models/meta.rb

@@ -0,0 +1,6 @@
+class Meta
+  include Mongoid::Document
+  field :length, type: String
+
+  embedded_in :address
+end

packages/forest_admin_datasource_mongoid/spec/dummy/app/models/post.rb

@@ -8,4 +8,7 @@ class Post
   has_many :comments, dependent: :destroy
   has_one :author
   has_and_belongs_to_many :tags
+  belongs_to :user
+
+  embeds_one :co_author
 end

packages/forest_admin_datasource_mongoid/spec/dummy/app/models/user.rb

@@ -5,4 +5,5 @@ class User
   field :name, type: String
   belongs_to :item, polymorphic: true
   embeds_many :addresses
+  embeds_one :address
 end