public function get_url_params() {
        $args = array(
            'id' => $this->course->id
        );
        if (!empty($this->instancefilter)) {
            $args['ifilter'] = $this->instancefilter;
        }
        if (!empty($this->rolefilter)) {
            $args['role'] = $this->rolefilter;
        }
        if ($this->searchfilter !== '') {
            $args['search'] = $this->searchfilter;
        }
        if (!empty($this->groupfilter)) {
            $args['filtergroup'] = $this->groupfilter;
        }
        if ($this->statusfilter !== -1) {
            $args['status'] = $this->statusfilter;
        }
        return $args;
    }