Implement has_one's embed objects

lib/active_model/serializer.rb

@@ -75,8 +75,8 @@ module ActiveModel
         if association.embed_ids?
           hash[association.key] = serialize_ids association
         elsif association.embed_objects?
-          # TODO
-          hash
+          associated_data = send(association.name)
+          hash[association.embedded_key] = association.build_serializer(associated_data).serializable_hash
         end
       end
     end

lib/active_model/serializer/associations.rb

@@ -37,6 +37,10 @@ module ActiveModel
         def key
           "#{name}_id"
         end
+
+        def embedded_key
+          name
+        end
       end
     end
   end

test/unit/active_model/serializer/has_one_test.rb

@@ -17,19 +17,33 @@ module ActiveModel
         assert_equal 'model', associations[0].name
       end
 
-      def test_associations_serialization_using_serializable_hash
+      def test_associations_embedding_ids_serialization_using_serializable_hash
         @model_serializer.class._associations[0].embed = :ids
         assert_equal({
           'attr2' => 'value2', 'attr3' => 'value3', 'model_id' => @model.model.object_id
         }, @model_serializer.serializable_hash)
       end
 
-      def test_associations_serialization_using_as_json
+      def test_associations_embedding_ids_serialization_using_as_json
         @model_serializer.class._associations[0].embed = :ids
         assert_equal({
           'attr2' => 'value2', 'attr3' => 'value3', 'model_id' => @model.model.object_id
         }, @model_serializer.as_json)
       end
+
+      def test_associations_embedding_objects_serialization_using_serializable_hash
+        @model_serializer.class._associations[0].embed = :objects
+        assert_equal({
+          'attr2' => 'value2', 'attr3' => 'value3', 'model' => { 'attr1' => 'v1', 'attr2' => 'v2' }
+        }, @model_serializer.serializable_hash)
+      end
+
+      def test_associations_embedding_objects_serialization_using_as_json
+        @model_serializer.class._associations[0].embed = :objects
+        assert_equal({
+          'attr2' => 'value2', 'attr3' => 'value3', 'model' => { 'attr1' => 'v1', 'attr2' => 'v2' }
+        }, @model_serializer.as_json)
+      end
     end
   end
 end