Add support for meta key

Test for meta_key serialization

lib/active_model/array_serializer.rb

@@ -35,6 +35,14 @@ module ActiveModel
       end
     end
 
+    def meta_key
+      @options[:meta_key].try(:to_sym) || :meta
+    end
+
+    def include_meta(hash)
+      hash[meta_key] = @options[:meta] if @options.has_key?(:meta)
+    end
+
     def as_json(*args)
       @options[:hash] = hash = {}
       @options[:unique_values] = {}
@@ -49,6 +57,8 @@ module ActiveModel
 
       if root = @options[:root]
         hash.merge!(root => array)
+        include_meta hash
+        hash
       else
         array
       end

lib/active_model/serializer.rb

@@ -227,6 +227,14 @@ module ActiveModel
       @options[:url_options] || {}
     end
 
+    def meta_key
+      @options[:meta_key].try(:to_sym) || :meta
+    end
+
+    def include_meta(hash)
+      hash[meta_key] = @options[:meta] if @options.has_key?(:meta)
+    end
+
     # Returns a json representation of the serializable
     # object including the root.
     def as_json(options={})
@@ -235,6 +243,7 @@ module ActiveModel
         @options[:unique_values] = {}
 
         hash.merge!(root => serializable_hash)
+        include_meta hash
         hash
       else
         serializable_hash

test/serializer_test.rb

@@ -1186,4 +1186,50 @@ class SerializerTest < ActiveModel::TestCase
       }
     }, actual)
   end
+
+  def test_meta_key_serialization
+    tag_serializer = Class.new(ActiveModel::Serializer) do
+      attributes :name
+    end
+
+    tag_class = Class.new(Model) do
+      def name
+        @attributes[:name]
+      end
+
+      define_method :active_model_serializer do
+        tag_serializer
+      end
+    end
+
+    serializable_array = Class.new(Array)
+
+    array = serializable_array.new
+    array << tag_class.new(:name => 'Rails')
+    array << tag_class.new(:name => 'Sinatra')
+
+    actual = array.active_model_serializer.new(array, :root => :tags, :meta => {:total => 10}).as_json
+
+    assert_equal({
+      :meta => {
+        :total => 10,
+      },
+      :tags => [
+        { :name => "Rails" },
+        { :name => "Sinatra" },
+      ]
+    }, actual)
+
+    actual = array.active_model_serializer.new(array, :root => :tags, :meta => {:total => 10}, :meta_key => 'meta_object').as_json
+
+    assert_equal({
+      :meta_object => {
+        :total => 10,
+      },
+      :tags => [
+        { :name => "Rails" },
+        { :name => "Sinatra" },
+      ]
+    }, actual)
+  end
 end