protected function fetch() {
        $row = $this->stmt->fetch(\PDO::FETCH_ASSOC);
        if (is_array($row) && !empty($row)) {
            $instance = $this->xpdo->call($this->class, '_loadInstance', array(& $this->xpdo, $this->class, $this->alias, $row));
            if ($instance === null) {
                $this->fetch();
            } else {
                $this->current = $instance;
            }
        } else {
            $this->current = null;
        }
    }