public function getNotifiableEntity(NotifiableInterface $notifiable)
    {
        $identifier = $this->generateIdentifier($notifiable);
        $class = ClassUtils::getRealClass(get_class($notifiable));
        $entity = $this->notifiableRepository->findOneBy(array(
            'identifier' => $identifier,
            'class' => $class
        ));

        if (!$entity) {
            $entity = new NotifiableEntity($identifier, $class);
            $this->om->persist($entity);
            $this->om->flush();
        }

        return $entity;
    }