protected function add(AnnouncementUnavailability $announcementUnavailability)
 {
     $q = $this->dao->prepare('INSERT INTO ' . $this->table() . ' SET DATE = :date, DATE_OPTION = :option, ANNOUNCEMENT_ID = :announcementId');
     $q->bindValue(':date', $announcementUnavailability->getDate());
     $q->bindValue(':option', $announcementUnavailability->getDateOption());
     $q->bindValue(':announcementId', $announcementUnavailability->getAnnouncementId(), PDO::PARAM_INT);
     $q->execute();
     $announcementUnavailability->setId($this->dao->lastInsertId());
 }