Add support for embed: :ids option for in associations

lib/active_model/serializer/adapter/json_api.rb

@@ -2,12 +2,14 @@ module ActiveModel
   class Serializer
     class Adapter
       class JsonApi < Adapter
-        def serializable_hash(options = {})
+        def serializable_hash(opts = {})
           @hash = serializer.attributes
 
           serializer.each_association do |name, association, options|
             @hash[:links] ||= {}
+            unless options[:embed] == :ids
               @hash[:linked] ||= {}
+            end
 
             if association.respond_to?(:each)
               add_links(name, association, options)
@@ -21,19 +23,25 @@ module ActiveModel
 
         def add_links(name, serializers, options)
           @hash[:links][name] ||= []
-          @hash[:linked][name] ||= []
           @hash[:links][name] += serializers.map(&:id)
+
+          unless options[:embed] == :ids
+            @hash[:linked][name] ||= []
             @hash[:linked][name] += serializers.map { |item| item.attributes(options) }
           end
+        end
 
         def add_link(name, serializer, options)
-          plural_name = name.to_s.pluralize.to_sym
-          @hash[:linked][plural_name] ||= []
-
           @hash[:links][name] = serializer.id
+
+          unless options[:embed] == :ids
+            plural_name = name.to_s.pluralize.to_sym
+
+            @hash[:linked][plural_name] ||= []
             @hash[:linked][plural_name].push serializer.attributes(options)
           end
         end
       end
     end
+  end
 end

test/adapter/json_api/has_many_embed_ids.rb

@@ -0,0 +1,31 @@
+require 'test_helper'
+
+module ActiveModel
+  class Serializer
+    class Adapter
+      class JsonApi
+        class HasManyEmbedIdsTest < Minitest::Test
+          def setup
+            @author = Author.new(name: 'Steve K.')
+            @first_post = Post.new(id: 1, title: 'Hello!!', body: 'Hello, world!!')
+            @second_post = Post.new(id: 2, title: 'New Post', body: 'Body')
+            @author.posts = [@first_post, @second_post]
+            @first_post.author = @author
+            @second_post.author = @author
+
+            @serializer = AuthorSerializer.new(@author)
+            @adapter = ActiveModel::Serializer::Adapter::JsonApi.new(@serializer)
+          end
+
+          def test_includes_comment_ids
+            assert_equal([1, 2], @adapter.serializable_hash[:links][:posts])
+          end
+
+          def test_no_includes_linked_comments
+            assert_nil @adapter.serializable_hash[:linked]
+          end
+        end
+      end
+    end
+  end
+end

test/fixtures/poro.rb

@@ -35,6 +35,7 @@ end
 
 Post = Class.new(Model)
 Comment = Class.new(Model)
+Author = Class.new(Model)
 
 PostSerializer = Class.new(ActiveModel::Serializer) do
   attributes :title, :body, :id
@@ -47,3 +48,9 @@ CommentSerializer = Class.new(ActiveModel::Serializer) do
 
   belongs_to :post
 end
+
+AuthorSerializer = Class.new(ActiveModel::Serializer) do
+  attributes :id, :name
+
+  has_many :posts, embed: :ids
+end