public function set_grading_evaluation_method($method) {
        global $DB;

        $evaluationlib = __DIR__ . '/eval/' . $method . '/lib.php';

        if (is_readable($evaluationlib)) {
            $this->evaluationinstance = null;
            $this->evaluation = $method;
            $DB->set_field('workshop', 'evaluation', $method, array('id' => $this->id));
            return true;
        }

        throw new coding_exception('Attempt to set a non-existing evaluation method.');
    }