function _generateId() {
        if ($this->getAttribute('id')) {
            return;
        }

        $id = $this->getName();
        $id = 'id_' . str_replace(array('qf_', '[', ']'), array('', '_', ''), $id);
        $id = clean_param($id, PARAM_ALPHANUMEXT);
        $this->updateAttributes(array('id' => $id));
    }