public function getNotificationRecipientIds()
    {
        $qb = $this->getEntityManager()->createQueryBuilder()
            ->select('n.recipient_id')
            ->distinct()
            ->from("Azine\EmailBundle\Entity\Notification", 'n')
            ->andWhere('n.sent is null');
        $results = $qb->getQuery()->execute();

        $ids = array();
        foreach ($results as $next) {
            $ids[] = $next['recipient_id'];
        }

        return $ids;
    }