Allow to set key for associations through options

lib/active_model/serializer/associations.rb

@@ -45,7 +45,7 @@ module ActiveModel
 
       class HasOne < Association
         def key
-          "#{name}_id"
+          @options[:key] || "#{name}_id"
         end
 
         def embedded_key
@@ -55,7 +55,7 @@ module ActiveModel
 
       class HasMany < Association
         def key
-          "#{name.singularize}_ids"
+          @options[:key] || "#{name.singularize}_ids"
         end
 
         def embedded_key

test/unit/active_model/serializer/has_many_test.rb

@@ -10,6 +10,7 @@ module ActiveModel
         @association.include = false
         @association.embed = :ids
         @association.options[:root] = nil
+        @association.options[:key] = nil
       end
 
       def test_associations_definition
@@ -30,6 +31,13 @@ module ActiveModel
         }, @post_serializer.as_json)
       end
 
+      def test_associations_embedding_ids_serialization_using_serializable_hash_and_key_from_options
+        @association.options[:key] = 'key'
+        assert_equal({
+          'title' => 'Title 1', 'body' => 'Body 1', 'key' => @post.comments.map { |c| c.object_id }
+        }, @post_serializer.serializable_hash)
+      end
+
       def test_associations_embedding_objects_serialization_using_serializable_hash
         @association.embed = :objects
         assert_equal({

test/unit/active_model/serializer/has_one_test.rb

@@ -10,6 +10,7 @@ module ActiveModel
         @association.include = false
         @association.embed = :ids
         @association.options[:root] = nil
+        @association.options[:key] = nil
       end
 
       def test_associations_definition
@@ -30,6 +31,13 @@ module ActiveModel
         }, @user_serializer.as_json)
       end
 
+      def test_associations_embedding_ids_serialization_using_serializable_hash_and_key_from_options
+        @association.options[:key] = 'key'
+        assert_equal({
+          'name' => 'Name 1', 'email' => 'mail@server.com', 'key' => @user.profile.object_id
+        }, @user_serializer.serializable_hash)
+      end
+
       def test_associations_embedding_objects_serialization_using_serializable_hash
         @association.embed = :objects
         assert_equal({