实体出现symfony2 doctrine2批处理错误

我正在尝试向DB插入许多实体。当我试图用这段代码插入示例5实体时,它可以毫无问题地工作。。。但当我在那里实现批处理方法时,它会导致以下错误:

(代码)

        if (!empty($invite_this_peopleArray)) {
            $batchSize = 20;
            $i = 0;
            foreach ($explodeInviteArray as $explodingUser) {
                ++$i;

                $notifiedUser=$userRepo->find($explodingUser);

                $notify=new Notify();
                $notify->setNotifyUser($user);
                $notify->setUser($notifiedUser);
                $notify->setStatus($lastStatus);
                $notify->setTyp('invite');
                $notify->setViewed(false);
                $notify->setAdInfo($name);

                $em->persist($notify);

                if (($i % $batchSize) === 0) {
                    $em->flush();
                    $em->clear(); // Detaches all objects from Doctrine!
                }            
            }
        }

错误:

A new entity was found through the relationship 'TB\NotifyBundle\Entity\Notify#notifyUser' that was not configured to cascade persist operations for entity: (nick of notify user user($user->getUsername())). To solve this issue: Either explicitly call EntityManager#persist() on this unknown entity or configure cascade persist this association in the mapping for example @ManyToOne(..,cascade={"persist"}).

请问有什么问题?

BTW:当我修改代码时,我只清除$notify和$notified用户喜欢:

                if (($i % $batchSize) === 0) {
                    $em->flush();
                    $em->clear($notify); // Detaches all objects from Doctrine!
                    $em->clear($notifiedUser); // Detaches all objects from Doctrine!
                }   

错误已经消失,但我试图插入4000行,我发现了这个错误:

Fatal error: Maximum execution time of 30 seconds exceeded in vendor/doctrine/orm/lib/Doctrine/ORM/UnitOfWork.php on line 514

当我尝试插入1000行时。

Fatal error: Allowed memory size of 134217728 bytes exhausted (tried to allocate 32 bytes)

(那么内存有泄漏吗?)