Support serializer and each_serializer in render json

Author: ggordon

README.md

@@ -94,6 +94,22 @@ member when the resource names are included in the `include` option.
   render @posts, include: 'authors,comments'
 ```
 
+### Specify a serializer
+
+If you wish to use a serializer other than the default, you can explicitly pass it to the renderer.
+
+#### 1. For a resource:
+
+```ruby
+  render json: @post, serializer: PostPreviewSerializer
+```
+
+#### 2. For an array resource:
+
+```ruby
+  render json: @posts, serializer: PaginatedSerializer, each_serializer: PostPreviewSerializer
+```
+
 ## Installation
 
 Add this line to your application's Gemfile:

lib/action_controller/serialization.rb

@@ -8,16 +8,25 @@ module Serialization
 
     ADAPTER_OPTION_KEYS = [:include, :root]
 
+    def get_serializer(resource, options)
+      @_serializer ||= if (serializer = options.delete :serializer)
+        options[:serializer] = options.delete :each_serializer
+        serializer
+      else
+        ActiveModel::Serializer.serializer_for(resource)
+      end
+    end
+
     [:_render_option_json, :_render_with_renderer_json].each do |renderer_method|
       define_method renderer_method do |resource, options|
-        serializer = ActiveModel::Serializer.serializer_for(resource)
 
-        if serializer
-          adapter_opts, serializer_opts =
-            options.partition { |k, _| ADAPTER_OPTION_KEYS.include? k }
+        adapter_opts, serializer_opts =
+          options.partition { |k, _| ADAPTER_OPTION_KEYS.include? k }.map { |h| Hash[h] }
+
+        if (serializer = get_serializer(resource, serializer_opts))
           # omg hax
-          object = serializer.new(resource, Hash[serializer_opts])
-          adapter = ActiveModel::Serializer.adapter.new(object, Hash[adapter_opts])
+          object = serializer.new(resource, serializer_opts)
+          adapter = ActiveModel::Serializer.adapter.new(object, adapter_opts)
           super(adapter, options)
         else
           super(resource, options)

lib/active_model/serializer/array_serializer.rb

@@ -6,7 +6,10 @@ class ArraySerializer
 
       def initialize(objects, options = {})
         @objects = objects.map do |object|
-          serializer_class = ActiveModel::Serializer.serializer_for(object)
+          serializer_class = options.fetch(
+            :serializer,
+            ActiveModel::Serializer.serializer_for(object)
+          )
           serializer_class.new(object)
         end
       end

test/action_controller/explicit_serializer_test.rb

@@ -0,0 +1,53 @@
+require 'test_helper'
+
+module ActionController
+  module Serialization
+    class ExplicitSerializerTest < ActionController::TestCase
+      class MyController < ActionController::Base
+        def render_using_explicit_serializer
+          @profile = Profile.new(name: 'Name 1',
+                                 description: 'Description 1',
+                                 comments: 'Comments 1')
+          render json: @profile, serializer: ProfilePreviewSerializer
+        end
+
+        def render_array_using_explicit_serializer
+          array = [
+            Profile.new(name: 'Name 1',
+                        description: 'Description 1',
+                        comments: 'Comments 1'),
+            Profile.new(name: 'Name 2',
+                        description: 'Description 2',
+                        comments: 'Comments 2')
+          ]
+          render json: array,
+                 serializer: PaginatedSerializer,
+                 each_serializer: ProfilePreviewSerializer
+        end
+      end
+
+      tests MyController
+
+      def test_render_using_explicit_serializer
+        get :render_using_explicit_serializer
+
+        assert_equal 'application/json', @response.content_type
+        assert_equal '{"name":"Name 1"}', @response.body
+      end
+
+      def test_render_array_using_explicit_serializer
+        get :render_array_using_explicit_serializer
+        assert_equal 'application/json', @response.content_type
+
+        expected = {
+          'paginated' => [
+            { 'name' => 'Name 1' },
+            { 'name' => 'Name 2' }
+          ]
+        }
+
+        assert_equal expected.to_json, @response.body
+      end
+    end
+  end
+end

test/fixtures/poro.rb

@@ -35,6 +35,12 @@ class ProfileSerializer < ActiveModel::Serializer
   urls :posts, :comments
 end
 
+class ProfilePreviewSerializer < ActiveModel::Serializer
+  attributes :name
+
+  urls :posts, :comments
+end
+
 Post = Class.new(Model)
 Comment = Class.new(Model)
 Author = Class.new(Model)
@@ -67,3 +73,9 @@ class ProfileSerializer < ActiveModel::Serializer
   belongs_to :writer
   has_many :articles
 end
+
+PaginatedSerializer = Class.new(ActiveModel::Serializer::ArraySerializer) do
+  def json_key
+    'paginated'
+  end
+end