function findBySubscriptions($event, $contact = '')
 {
     if (!$contact instanceof Contact) {
         $contact_id = logged_user()->getId();
     } else {
         $contact_id = $contact->getId();
     }
     return ObjectSubscriptions::findOne(array('conditions' => array('`contact_id` = ? AND object_id = ?', $contact_id, $event)));
 }