Make Associations in root work with ArraySerializer

Closes #414

lib/active_model/array_serializer.rb

@@ -37,5 +37,27 @@ module ActiveModel
       end
     end
     alias_method :serializable_object, :serializable_array
+
+    def serializable_data
+      embedded_in_root_associations.merge!(super)
+    end
+
+    def embedded_in_root_associations
+      hash = {}
+      @object.map do |item|
+        serializer_class = @each_serializer || Serializer.serializer_for(item) || DefaultSerializer
+        associations = serializer_class._associations
+        serializer = serializer_class.new(item, @options)
+        included_associations = serializer.filter(associations.keys)
+        associations.each do |(name, association)|
+          if included_associations.include? name
+            if association.embed_in_root?
+              hash[association.embedded_key] = serializer.serialize association
+            end
+          end
+        end
+      end
+      hash
+    end
   end
 end

test/integration/action_controller/serialization_test.rb

@@ -193,5 +193,42 @@ module ActionController
         assert_equal '{"my":[{"name":"Name 1","description":"Description 1"}]}', @response.body
       end
     end
+
+    class ArrayEmbedingSerializerTest < ActionController::TestCase
+      def setup
+        super
+        @association = UserSerializer._associations[:profile]
+        @old_association = @association.dup
+      end
+
+      def teardown
+        super
+        UserSerializer._associations[:profile] = @old_association
+      end
+
+      class MyController < ActionController::Base
+        def initialize(*)
+          super
+          @user = User.new({ name: 'Name 1', email: 'mail@server.com', gender: 'M' })
+        end
+        attr_reader :user
+
+        def render_array_embeding_in_root
+          render json: [@user]
+        end
+      end
+
+      tests MyController
+
+      def test_render_array_embeding_in_root
+        @association.embed = :ids
+        @association.embed_in_root = true
+
+        get :render_array_embeding_in_root
+        assert_equal 'application/json', @response.content_type
+
+        assert_equal("{\"my\":[{\"name\":\"Name 1\",\"email\":\"mail@server.com\",\"profile_id\":#{@controller.user.profile.object_id}}],\"profiles\":[{\"name\":\"N1\",\"description\":\"D1\"}]}", @response.body)
+      end
+    end
   end
 end