Use controller name as root when serializing an array and not root is defined

lib/action_controller/serialization.rb

@@ -71,6 +71,7 @@ module ActionController
       return unless serializer
 
       options[:scope] = serialization_scope unless options.has_key?(:scope)
+      options[:resource_name] = self.controller_name if resource.respond_to?(:to_ary)
 
       serializer.new(resource, options)
     end

lib/active_model/array_serializer.rb

@@ -16,6 +16,7 @@ module ActiveModel
       @object          = object
       @root            = options[:root]
       @root            = self.class._root if @root.nil?
+      @root            = options[:resource_name] if @root.nil?
       @meta_key        = options[:meta_key] || :meta
       @meta            = options[@meta_key]
       @each_serializer = options[:each_serializer]