protected function delete_grades() {
        global $CFG;

        $result = grade_update('mod/assign',
                               $this->get_course()->id,
                               'mod',
                               'assign',
                               $this->get_instance()->id,
                               0,
                               null,
                               array('deleted'=>1));
        return $result == GRADE_UPDATE_OK;
    }
protected function delete_grades() {
        global $CFG;

        $result = grade_update('mod/assign',
                               $this->get_course()->id,
                               'mod',
                               'assign',
                               $this->get_instance()->id,
                               0,
                               null,
                               array('deleted'=>1));
        return $result == GRADE_UPDATE_OK;
    }
protected function delete_grades ( ) { global $ CFG ; $ result = grade_update ( 'mod/assign' , $ this -> get_course ( ) -> id , 'mod' , 'assign' , $ this -> get_instance ( ) -> id , 0 , null , array ( 'deleted' => 1 ) ) ; return $ result == GRADE_UPDATE_OK ; }
Delete all grades from the gradebook for this assignment.

@return bool
Delete all grades from the gradebook for this assignment .