# File lib/mongo_mapper/plugins/partial_updates.rb, line 21
      def fields_for_partial_update
        raise PartialUpdatesDisabledError if !partial_updates

        Hash.new.tap do |hash|
          attrs = _dealiased_attributes

          hash[:set_fields] = Array.new.tap do |array|
            attrs.each do |key, value|
              if !@_last_saved_attributes.include?(key) ||
                  @_last_saved_attributes[key] != value
                array << key
              end
            end
          end

          hash[:unset_fields] = @_last_saved_attributes.keys - attrs.keys
        end
      end