$subpluginelementfiles->set_source_sql('SELECT id AS gradeid from {assign_grades} where id = :gradeid',array('gradeid'=>backup::VAR_PARENTID));
$subpluginelementfiles->set_source_sql('SELECT id AS gradeid from {assign_grades} where id = :'.self::GRADEID,array(self::GRADEID=>backup::VAR_PARENTID));