Symfony 3.4未定义属性：条令\ORM\EntityManager:：$flush

我正在尝试创建一个几乎没有成功的服务

class NotificationService {

public $manager;

public function __construct($manager) {

    $this->manager = $manager;
}

public function set($user, $type, $typeId, $extra = null){

    $em = $this->manager;

    $notification = new Notification();
    $notification->setUser($user);
    $notification->setType($type);
    $notification->setTypeId($typeId);
    $notification->setReaded(0);
    $notification->setCreatedAt(new \DateTime('now'));
    $notification->setExtra($extra);

    $em->persist($notification);
    $flush = $em->flush;

    if($flush == null){
        $status = true;
    }else{
        $status = false;
    }

    return $status;
}

}

这是我的服务。yml：

app.notification_service:
    class: AppBundle\Services\NotificationService
    public: true
    arguments: ['@doctrine.orm.entity_manager']

我打电话给LikeControl的服务。这样做的目的是在有人喜欢他们的帖子时通知会员：

public function likeAction(Request $request){
    $user = $this->getUser();
    $id = $request->get('id');

    $em = $this->getDoctrine()->getManager();

    $publication = $em->getRepository('BackendBundle:Publication')->find($id);

    $like = new Like();
    $like->setUser($user);
    $like->setPublication($publication);

    $em->persist($like);
    $flush = $em->flush();

    if($flush == NULL){
        $notification = $this->get('app.notification_service');
        $notification->set($publication->getUser(), 'like', $user->getId(), $publication->getId());

        $status = 'You like this post';
    }else{
        $status = 'Could not save the like.';
    }

    return new JsonResponse(['status' => $status]);
}

当我测试它时，它不起作用。相反，我得到一个异常，EntityManager无法识别flush方法：

未定义的属性：条令\ORM\EntityManager:：$flush

有人能告诉我怎么解决这个问题吗？谢谢。

您必须写下：

$flush=$em->flush（）

相反：

$flush=$em->flush
$em->flush（）；帕伦夫妇很重要，我已经想了4个小时了。我觉得自己像个白痴！谢谢你的帮助。