public function executeJson(AgaviRequestDataHolder $rd)
 {
     if ($this->hasAttribute('categories')) {
         $categories = $this->getAttribute('categories', array());
         $json = new AppKitExtJsonDocument();
         $json->setAttribute(AppKitExtJsonDocument::ATTR_AUTODISCOVER);
         $json->setMeta(AppKitExtJsonDocument::PROPERTY_ID, 'catid');
         $json->setData($categories);
         $json->setSuccess(true);
         return $json->getJson();
     }
 }