Merge pull request #1213 from AutoCloud/type_setting

Add Serializer 'type' directive to control type field, for
 use by the JsonApi adapter

lib/active_model/serializer.rb

@@ -46,6 +46,10 @@ module ActiveModel
       super
     end
 
+    def self.type(type)
+      self._type = type
+    end
+
     def self.attributes(*attrs)
       attrs = attrs.first if attrs.first.class == Array
 
@@ -122,6 +126,7 @@ module ActiveModel
     end
 
     attr_accessor :object, :root, :meta, :meta_key, :scope
+    class_attribute :_type, instance_writer: false
 
     def initialize(object, options = {})
       self.object = object

lib/active_model/serializer/adapter/json_api.rb

@@ -71,6 +71,7 @@ module ActiveModel
         end
 
         def resource_identifier_type_for(serializer)
+          return serializer._type if serializer._type
           if ActiveModel::Serializer.config.jsonapi_resource_type == :singular
             serializer.object.class.model_name.singular
           else