Adds support for meta attribute

Currently, 0.10.0.pre doesn't support `meta` option in `render`. This
way, there's no way to support features such as pagination. `0.9` had
this feature in place.

This adds support for it, as well as fixes small things in README.md.

This won't support `meta` in array responses because arrays don't have
keys, obviously. Also, the response should have a `root` key, otherwise
no `meta` will be included.

In some cases, for example using JsonApi, ArraySerializer will result in
a response with a `root`. In that case, `meta` will be included.

CHANGELOG.md

@@ -0,0 +1,3 @@
+### 0.10.0
+
+  * adds support for `meta` and `meta_key` [@kurko]

README.md

@@ -54,18 +54,17 @@ end
 ```
 
 Generally speaking, you as a user of AMS will write (or generate) these
-serializer classes. By default, they will use the JsonApiAdapter, implemented
-by AMS. If you want to use a different adapter, such as a HalAdapter, you can
+serializer classes. If you want to use a different adapter, such as a JsonApi, you can
 change this in an initializer:
 
 ```ruby
-ActiveModel::Serializer.config.adapter = ActiveModel::Serializer::Adapter::HalAdapter
+ActiveModel::Serializer.config.adapter = ActiveModel::Serializer::Adapter::JsonApi
 ```
 
 or
 
 ```ruby
-ActiveModel::Serializer.config.adapter = :hal
+ActiveModel::Serializer.config.adapter = :json_api
 ```
 
 You won't need to implement an adapter unless you wish to use a new format or
@@ -99,15 +98,6 @@ end
 In this case, Rails will look for a serializer named `PostSerializer`, and if
 it exists, use it to serialize the `Post`.
 
-### Built in Adapters
-
-The `:json_api` adapter will include the associated resources in the `"linked"`
-member when the resource names are included in the `include` option.
-
-```ruby
-  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.
@@ -129,6 +119,46 @@ render json: @posts, each_serializer: PostPreviewSerializer
 render json: @posts, serializer: PaginatedSerializer, each_serializer: PostPreviewSerializer
 ```
 
+### Meta
+
+If you want a `meta` attribute in your response, specify it in the `render`
+call:
+
+```ruby
+render json: @post, meta: { total: 10 }
+```
+
+The key can be customized using `meta_key` option.
+
+```ruby
+render json: @post, meta: { total: 10 }, meta_key: "custom_meta"
+```
+
+`meta` will only be included in your response if there's a root. For instance,
+it won't be included in array responses.
+
+### Root key
+
+If you want to define a custom root for your response, specify it in the `render`
+call:
+
+```ruby
+render json: @post, root: "articles"
+```
+
+### Built in Adapters
+
+#### JSONAPI
+
+This adapter follows the format specified in
+[jsonapi.org/format](http://jsonapi.org/format). It will include the associated
+resources in the `"linked"` member when the resource names are included in the
+`include` option.
+
+```ruby
+  render @posts, include: 'authors,comments'
+```
+
 ## Installation
 
 Add this line to your application's Gemfile:

lib/active_model/serializer.rb

@@ -114,11 +114,13 @@ def self.root_name
       name.demodulize.underscore.sub(/_serializer$/, '') if name
     end
 
-    attr_accessor :object, :root
+    attr_accessor :object, :root, :meta, :meta_key
 
     def initialize(object, options = {})
       @object = object
       @root   = options[:root] || (self.class._root ? self.class.root_name : false)
+      @meta   = options[:meta]
+      @meta_key = options[:meta_key]
     end
 
     def json_key

lib/active_model/serializer/adapter.rb

@@ -18,7 +18,8 @@ def serializable_hash(options = {})
       end
 
       def as_json(options = {})
-        serializable_hash(options)
+        hash = serializable_hash(options)
+        include_meta(hash)
       end
 
       def self.create(resource, options = {})
@@ -30,6 +31,27 @@ def self.create(resource, options = {})
       def self.adapter_class(adapter)
         "ActiveModel::Serializer::Adapter::#{adapter.to_s.classify}".safe_constantize
       end
+
+      private
+
+      def meta
+        serializer.meta if serializer.respond_to?(:meta)
+      end
+
+      def meta_key
+        serializer.meta_key || "meta"
+      end
+
+      def root
+        serializer.json_key
+      end
+
+      def include_meta(json)
+        puts "meta: #{meta.inspect}" if $debug
+        puts "root: #{root.inspect}" if $debug
+        json[meta_key] = meta if meta && root
+        json
+      end
     end
   end
 end

lib/active_model/serializer/array_serializer.rb

@@ -4,6 +4,8 @@ class ArraySerializer
       include Enumerable
       delegate :each, to: :@objects
 
+      attr_reader :meta, :meta_key
+
       def initialize(objects, options = {})
         @objects = objects.map do |object|
           serializer_class = options.fetch(
@@ -12,6 +14,8 @@ def initialize(objects, options = {})
           )
           serializer_class.new(object)
         end
+        @meta     = options[:meta]
+        @meta_key = options[:meta_key]
       end
 
       def json_key

test/action_controller/serialization_test.rb

@@ -37,6 +37,18 @@ def render_array_using_implicit_serializer
           ]
           render json: array
         end
+
+        def render_array_using_implicit_serializer_and_meta
+          old_adapter = ActiveModel::Serializer.config.adapter
+
+          ActiveModel::Serializer.config.adapter = ActiveModel::Serializer::Adapter::JsonApi
+          array = [
+            Profile.new({ name: 'Name 1', description: 'Description 1', comments: 'Comments 1' })
+          ]
+          render json: array, meta: { total: 10 }
+        ensure
+          ActiveModel::Serializer.config.adapter = old_adapter
+        end
       end
 
       tests MyController
@@ -87,6 +99,13 @@ def test_render_array_using_implicit_serializer
 
         assert_equal expected.to_json, @response.body
       end
+
+      def test_render_array_using_implicit_serializer_and_meta
+        get :render_array_using_implicit_serializer_and_meta
+
+        assert_equal 'application/json', @response.content_type
+        assert_equal '{"profiles":[{"name":"Name 1","description":"Description 1"}],"meta":{"total":10}}', @response.body
+      end
     end
   end
 end

test/serializers/meta_test.rb

@@ -0,0 +1,77 @@
+require 'test_helper'
+
+module ActiveModel
+  class Serializer
+    class MetaTest < Minitest::Test
+      def setup
+        @blog = Blog.new(id: 1,
+                         name: 'AMS Hints',
+                         writer: Author.new(id: 2, name: "Steve"),
+                         articles: [Post.new(id: 3, title: "AMS")])
+      end
+
+      def test_meta_is_present_with_root
+        adapter = load_adapter(root: "blog", meta: {total: 10})
+        expected = {
+          "blog" => {
+            id: 1,
+            title: "AMS Hints"
+          },
+          "meta" => {
+            total: 10
+          }
+        }
+        assert_equal expected, adapter.as_json
+      end
+
+      def test_meta_is_not_included_when_root_is_missing
+        adapter = load_adapter(meta: {total: 10})
+        expected = {
+          id: 1,
+          title: "AMS Hints"
+        }
+        assert_equal expected, adapter.as_json
+      end
+
+      def test_meta_key_is_used
+        adapter = load_adapter(root: "blog", meta: {total: 10}, meta_key: "haha_meta")
+        expected = {
+          "blog" => {
+            id: 1,
+            title: "AMS Hints"
+          },
+          "haha_meta" => {
+            total: 10
+          }
+        }
+        assert_equal expected, adapter.as_json
+      end
+
+      def test_meta_is_not_used_on_arrays
+        serializer = ArraySerializer.new([@blog], root: "blog", meta: {total: 10}, meta_key: "haha_meta")
+        adapter = ActiveModel::Serializer::Adapter::Json.new(serializer)
+        expected = [{
+          id: 1,
+          name: "AMS Hints",
+          writer: {
+            id: 2,
+            name: "Steve"
+          },
+          articles: [{
+            id: 3,
+            title: "AMS",
+            body: nil
+          }]
+        }]
+        assert_equal expected, adapter.as_json
+      end
+
+      private
+
+      def load_adapter(options)
+        serializer = AlternateBlogSerializer.new(@blog, options)
+        ActiveModel::Serializer::Adapter::Json.new(serializer)
+      end
+    end
+  end
+end