changed_attributes

# File activerecord/lib/active_record/attribute_methods/dirty.rb, line 56
      def changed_attributes
        # This should only be set by methods which will call changed_attributes
        # multiple times when it is known that the computed value cannot change.
        if defined?(@cached_changed_attributes)
          @cached_changed_attributes
        else
          super.reverse_merge(attributes_changed_in_place).freeze
        end
      end