public function init($selfitemisempty = false) {
        global $DB;

        $roleids = explode(',', get_config('moodle', 'gradebookroles'));

        $this->items = array();
        foreach ($roleids as $roleid) {
            // Keeping the first user appearance.
            $this->items = $this->items + get_role_users(
                $roleid, $this->context, false, '',
                'u.id, u.lastname, u.firstname', null, $this->groupid,
                $this->perpage * $this->page, $this->perpage
            );
        }
        $this->item = $DB->get_record('course', array('id' => $this->courseid));
    }