public function getLastNotificationDate($recipientId)
    {
        $qb = $this->getEntityManager()->createQueryBuilder()
            ->select('max(n.sent)')
            ->from("Azine\EmailBundle\Entity\Notification", 'n')
            ->andWhere('n.recipient_id = :recipientId')
            ->setParameter('recipientId', $recipientId);
        $results = $qb->getQuery()->execute();
        if (null === $results[0][1]) {
            // the user has not received any notifications yet ever
            $lastNotification = new \DateTime('@0');
        } else {
            $lastNotification = new \DateTime($results[0][1]);
        }

        return $lastNotification;
    }