public function toArray()
    {
        $array = array();
        foreach ($this->_data as $key => $value) {
            if (is_object($value)) {
                $array[$key] = $value->asArray();   <----- must be $array[$key] = $value->toArray();
            } else {
                $array[$key] = $value;
            }
        }
        return $array;
    }