public function getUrl()
    {
        if (!$this->isSortable()) {
            return '';
        }

        $params = ['sort_key' => $this->key];

        if ($this->isSortKey()) {
            $params['sort_order'] = $this->request->input('sort_order') == 'desc' ? 'asc' : 'desc';
        }

        return '?'.http_build_query($params + $this->request->all());
    }