app\models\Document::toArray PHP Method

    public function toArray()
    {
        $array = parent::toArray();
        if (empty($this->visible) || in_array('url', $this->visible)) {
            $array['url'] = $this->getUrl();
        }
        if (empty($this->visible) || in_array('preview_url', $this->visible)) {
            $array['preview_url'] = $this->getPreviewUrl();
        }
        return $array;
    }