public function addItems(array $items, $where = '')
    {
        foreach (array_keys($items) as $k) {
            if (!is_int($k) && $this->hasItem($k)) {
                unset($items[$k]);
            }
        }
        if (!empty($items)) {
            $this->setItems($items, $where);
        }

        return $this;
    }