Grape formatter feature requested in rails-api#1268

 - adds handling for when the returned resource is not serializable via ams
 - fix for when resource is an Array
 - fixing last checkin
 - Adds intellij .idea file to .gitignore
 - Moves grape include to grape namespace. Changes Enumerable to Array because a plain hash is enumerable.
 - rubocop corrections
 - Rebased and squashed commits, resubmitted to CI
 - Remove .idea from gitignore
 - Add integration test

active_model_serializers.gemspec

@@ -47,4 +47,5 @@ Gem::Specification.new do |spec|
 
   spec.add_development_dependency 'bundler', '~> 1.6'
   spec.add_development_dependency 'timecop', '~> 0.7'
+  spec.add_development_dependency 'grape', '~> 0.13.0'
 end

docs/README.md

@@ -16,6 +16,7 @@ This is the documentation of AMS, it's focused on the **0.10.x version.**
 - [How to add pagination links](howto/add_pagination_links.md)
 - [Using AMS Outside Of Controllers](howto/outside_controller_use.md)
 - [How to use JSON API with Ember](howto/ember-and-json-api.md)
+- [Grape](howto/grape.md)
 
 ## Getting Help
 

docs/howto/grape.md

@@ -0,0 +1,27 @@
+# Integration with Grape
+
+To add Grape support, `require 'grape/active_model_serializers'` in the base of your Grape endpoints like so:
+
+```ruby
+module Example
+  class Dummy < Grape::API
+    require 'grape/active_model_serializers'
+    mount Example::V1::Base
+  end
+end
+```
+
+Then add the formatter and helpers to the endpoints (a `Defaults` module is used here which would be included in all endpoints):
+
+```ruby
+module Example::V1::Defaults
+  extend ActiveSupport::Concern
+
+  included do
+    formatter :json, Grape::Formatters::ActiveModelSerializers
+    helpers Grape::Helpers::ActiveModelSerializers
+  end
+
+end
+```
+

lib/grape/active_model_serializers.rb

@@ -0,0 +1,6 @@
+# To add grape support, require 'grape/active_model_serializers' in the base of your grape endpoints
+# Then add 'formatter :json, Grape::Formatters::ActiveModelSerializers' to the endpoints
+# Then add 'helpers Grape::Helpers::ActiveModelSerializers' to the endpoints
+require 'active_model_serializers'
+require 'grape/formatters/active_model_serializers'
+require 'grape/helpers/active_model_serializers'

lib/grape/formatters/active_model_serializers.rb

@@ -0,0 +1,16 @@
+# A grape response formatter that can be used as 'formatter :json, Grape::Formatters::ActiveModelSerializers'
+#
+# Serializer options can be passed as a hash from your grape endpoint using env[:active_model_serializer_options],
+# or better yet user the render helper in Grape::Helpers::ActiveModelSerializers
+module Grape
+  module Formatters
+    module ActiveModelSerializers
+      def self.call(resource, env)
+        return resource.to_json unless resource.is_a?(Array) || resource.respond_to?(:model_name)
+        serializer_options = {}
+        serializer_options.merge!(env[:active_model_serializer_options]) if env[:active_model_serializer_options]
+        ActiveModel::SerializableResource.new(resource, serializer_options).to_json
+      end
+    end
+  end
+end

lib/grape/helpers/active_model_serializers.rb

@@ -0,0 +1,16 @@
+# Helpers can be included in your grape endpoint as: helpers Grape::Helpers::ActiveModelSerializers
+module Grape
+  module Helpers
+    module ActiveModelSerializers
+      # A convenience method for passing ActiveModelSerializer serializer options
+      #
+      # Example: To include relationships in the response: render(post, include: ['comments'])
+      #
+      # Example: To include pagination meta data: render(posts, meta: { page: posts.page, total_pages: posts.total_pages })
+      def render(resource, active_model_serializer_options = {})
+        env[:active_model_serializer_options] = active_model_serializer_options
+        resource
+      end
+    end
+  end
+end

test/grape_test.rb

@@ -0,0 +1,50 @@
+require 'test_helper'
+require 'securerandom'
+require 'grape'
+require 'grape/active_model_serializers'
+
+class ActiveModelSerializers::GrapeTest < Minitest::Test
+  include Rack::Test::Methods
+
+  class GrapeTest < Grape::API
+    format :json
+    formatter :json, Grape::Formatters::ActiveModelSerializers
+    helpers Grape::Helpers::ActiveModelSerializers
+
+    resources :grape do
+      get '/render' do
+        render ARModels::Post.new(title: 'Dummy Title', body: 'Lorem Ipsum')
+      end
+
+      get '/render_with_json_api' do
+        post = ARModels::Post.new(title: 'Dummy Title', body: 'Lorem Ipsum')
+        render(
+          post,
+          meta: { page: 1, total_pages: 2 },
+          adapter: :json_api
+        )
+      end
+    end
+  end
+
+  def app
+    GrapeTest.new
+  end
+
+  def test_formatter_returns_json
+    get '/grape/render'
+    assert last_response.ok?
+    assert JSON.parse(last_response.body)
+  end
+
+  def test_render_helper_passes_through_options_correctly
+    get '/grape/render_with_json_api'
+
+    post = ARModels::Post.new(title: 'Dummy Title', body: 'Lorem Ipsum')
+    serializer = ARModels::PostSerializer.new(post)
+    adapter = ActiveModel::Serializer::Adapter::JsonApi.new(serializer, meta: { page: 1, total_pages: 2 })
+
+    assert last_response.ok?
+    assert_equal adapter.to_json, last_response.body
+  end
+end