public function save(PropelPDO $con = null)
 {
     if ($this->user_id == null) {
         $afUser = sfContext::getInstance()->getUser()->getAppFlowerUser();
         if (!$afUser->isAnonymous()) {
             $this->setUserId($afUser->getId());
             parent::save($con);
         }
     } else {
         parent::save($con);
     }
 }