Throw a descriptive error if attempting to serialize an array with Serializer not ArraySerializer #143

lib/action_controller/serialization.rb

@@ -44,6 +44,11 @@ module ActionController
         (json.respond_to?(:active_model_serializer) && json.active_model_serializer)
 
       if json.respond_to?(:to_ary)
+        unless serializer <= ActiveModel::ArraySerializer
+          raise ArgumentError.new("#{serializer.name} is not an ArraySerializer. " +
+             "You may want to use the :each_serializer option instead.")
+        end
+
         if options[:root] != false && serializer.root != false
           # default root element for arrays is serializer's root or the controller name
           # the serializer for an Array is ActiveModel::ArraySerializer

test/serialization_test.rb

@@ -152,6 +152,10 @@ class RenderJsonTest < ActionController::TestCase
       render :json => [Object.new], :each_serializer => CustomSerializer
     end
 
+    def render_json_array_with_wrong_option
+      render :json => [Object.new], :serializer => CustomSerializer
+    end
+
     def render_json_with_links
       render :json => HypermediaSerializable.new
     end
@@ -286,6 +290,12 @@ class RenderJsonTest < ActionController::TestCase
     assert_match '{"test":[{"hello":true}]}', @response.body
   end
 
+  def test_render_json_array_with_wrong_option
+    assert_raise ArgumentError do
+      get :render_json_array_with_wrong_option
+    end
+  end
+
   def test_render_json_with_links
     get :render_json_with_links
     assert_match '{"link":"http://www.nextangle.com/hypermedia"}', @response.body