private function validate($data)
 {
     $album = $this->album_model->getById($this->id);
     // check url
     $parent_id = $album['parent_id'];
     if ($data['url'] != null) {
         if ($this->album_model->urlExists($data['url'], $this->id, $parent_id)) {
             $this->errors['url'] = _w('URL is in use');
         }
     }
     return empty($this->errors);
 }