public function get_submission_by_author($authorid) {
        global $DB;

        if (empty($authorid)) {
            return false;
        }
        $authorfields      = user_picture::fields('u', null, 'authoridx', 'author');
        $gradeoverbyfields = user_picture::fields('g', null, 'gradeoverbyx', 'gradeoverby');
        $sql = "SELECT s.*, $authorfields, $gradeoverbyfields
                  FROM {workshop_submissions} s
            INNER JOIN {user} u ON (s.authorid = u.id)
             LEFT JOIN {user} g ON (s.gradeoverby = g.id)
                 WHERE s.example = 0 AND s.workshopid = :workshopid AND s.authorid = :authorid";
        $params = array('workshopid' => $this->id, 'authorid' => $authorid);
        return $DB->get_record_sql($sql, $params);
    }