Refactor and consolidate serializer option setup

lib/action_controller/serialization.rb

@@ -51,31 +51,14 @@ module ActionController
     end
 
     module RenderJsonOverride
-      def _render_option_json(json, options)
-        options = default_serializer_options.merge(options) if default_serializer_options
+      def _render_option_json(resource, options)
+        json = ActiveModel::Serializer.build_json(self, resource, options)
 
-        serializer = options.delete(:serializer) ||
-          (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
-            options[:root] ||= serializer.root || controller_name
-          end
+        if json
+          super(json, options)
+        else
+          super
         end
-
-        if serializer
-          options[:scope] = serialization_scope unless options.has_key?(:scope)
-          options[:url_options] = url_options
-          json = serializer.new(json, options)
-        end
-        super
       end
     end
 

lib/active_model/serializer.rb

@@ -255,6 +255,35 @@ module ActiveModel
         self._root = name
       end
       alias_method :root=, :root
+
+      def build_json(controller, resource, options)
+        default_options = controller.send(:default_serializer_options) || {}
+        options = default_options.merge(options || {})
+
+        serializer = options.delete(:serializer) ||
+          (resource.respond_to?(:active_model_serializer) &&
+           resource.active_model_serializer)
+
+        return serializer unless serializer
+
+        if resource.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
+            # the serializer for an Array is ActiveModel::ArraySerializer
+            options[:root] ||= serializer.root || controller.controller_name
+          end
+        end
+
+        options[:scope] = controller.serialization_scope unless options.has_key?(:scope)
+        options[:scope_name] = controller._serialization_scope
+        options[:url_options] = controller.url_options
+
+        serializer.new(resource, options)
+      end
     end
 
     attr_reader :object, :options

lib/active_model/serializer/responder.rb

@@ -1,39 +1,16 @@
 module ActiveModel
   class Serializer
     class Responder < ::ActionController::Responder #:nodoc:
-      attr_reader :serializer
 
     protected
       def display(resource, given_options = {})
         if format != :json
           super
         else
-          default_options = controller.send(:default_serializer_options)
-          options = self.options.reverse_merge(default_options || {})
+          json = Serializer.build_json(controller, resource, options)
 
-          serializer = options[:serializer] ||
-            (resource.respond_to?(:active_model_serializer) &&
-             resource.active_model_serializer)
-
-          if resource.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
-              options[:root] ||= serializer.root || controller.send(:controller_name)
-            end
-          end
-
-          if serializer
-            serialization_scope = controller.send(:serialization_scope)
-            options[:scope] = serialization_scope unless options.has_key?(:scope)
-            options[:scope_name] = controller.send(:_serialization_scope)
-            options[:url_options] = controller.send(:url_options)
-            render(given_options.merge(self.options).merge(:json => serializer.new(resource, options)))
+          if json
+            render given_options.merge(options).merge(:json => json)
           else
             super
           end