尝试保存其他实体时 Doctrine 事件侦听器中的无限循环

我希望每次新的时候Distance保存实体（从 Place_A 到 Place_B），反向距离（从 Place_B 到 Place_A）也被插入到数据库中 https://stackoverflow.com/q/30569463/2516943.

我的问题是以下侦听器无限循环（因此是计数器）：

class Listener
{
    public $count;

    public function prePersist(LifecycleEventArgs $eventArgs)
    {
        if ($this->count > 5) {
            die();
        }

        $entity = $eventArgs->getEntity();

        if ($entity instanceof Distance) {
            // $this->created = microtime(true) in Distance's constructor
            echo 'Entity created at ' . $entity->created;

            if ($entity->isReverse) {
                echo " is reverse\n";
            } else {
                echo " is not reverse\n";
                $this->count++;

                $reverse = new Distance();
                $reverse->setOrigin($entity->getDestination());
                $reverse->setDestination($entity->getOrigin());
                $reverse->set($entity->getMiles());
                $reverse->isReverse = true;

                $em = $eventArgs->getEntityManager();
                $em->persist($reverse);
                $em->flush();
            }
        }
    }
}

Output:

Entity created at 1433168310.8787 is not reverse
Entity created at 1433168310.9073 is reverse
Entity created at 1433168310.8787 is not reverse
Entity created at 1433168310.9078 is reverse
Entity created at 1433168310.8787 is not reverse
Entity created at 1433168310.908 is reverse
Entity created at 1433168310.8787 is not reverse
Entity created at 1433168310.9084 is reverse
Entity created at 1433168310.8787 is not reverse
Entity created at 1433168310.9087 is reverse
Entity created at 1433168310.8787 is not reverse

就像原始实体（创建时间以 8787 结尾）被保留了无数次。

以防万一，如果我删除对$em->flush，我正确地得到以下输出：

Entity created at 1433167824.2552 is not reverse
Entity created at 1433167824.2947 is reverse

但随后出现异常，表示没有参数绑定到插入查询。 Symfony 的分析器证实了这一点：

INSERT INTO Distance (
    miles, origin_id, destination_id
) 
VALUES 
(?, ?, ?)
Parameters: { }

我想了解为什么我的侦听器不能按我的预期工作，以及如何修复它。

根据要求，这里有更多代码。一切都源于一个Place除了输入地名之外，我还可以添加/删除/编辑到其他地方的距离集合Places.

// PlaceController::updateAction
public function updateAction(Request $request, $id)
{
    $em = $this->getDoctrine()->getManager();

    $entity = $em->getRepository('MyBundle:Place')->find($id);
    if (! $entity) {
        throw $this->createNotFoundException('Unable to find Place entity.');
    }

    $deleteForm = $this->createDeleteForm($id);
    $editForm = $this->createForm(new PlaceType(), $entity, array(
        'action' => $this->generateUrl('update_place', array('id' => $entity->getId())),
        'method' => 'PUT'
    ));
    $editForm->add('submit', 'submit', array('label' => 'panel.button.save'));

    $editForm->handleRequest($request);

    if ($editForm->isValid()) {
        $em->flush();

    return array(
        'entity' => $entity,
        'form' => $editForm->createView(),
        'delete_form' => $deleteForm->createView(),
    );
}

// PlaceType::buildForm
public function buildForm(FormBuilderInterface $builder, array $options)
{
    $Place = $builder->getData();

    $builder
        ->add(
            'name',
            'text',
            [
                'label' => 'object.place.name'
            ]
        )
        ->add(
            'distancesTo',
            'collection',
            [
                'label' => 'object.place.distance.plural',
                'type' => new DistanceType(),
                'by_reference' => false,
                'allow_add' => true,
                'allow_delete' => true,
                'options' => [
                    'required' => false,
                    'origin' => $Place->getId() ? $Place : null
                ]
            ]
        );
}

你不应该在 prePersist 中使用 $em->flush() ，它受到 Doctrine 的限制：http://doctrine-orm.readthedocs.org/en/latest/reference/events.html#reference-events-implementing-listeners http://doctrine-orm.readthedocs.org/en/latest/reference/events.html#reference-events-implementing-listeners

有关于 preUpdate 的信息，但相同的情况（循环）适用于 prePesist 调用

9.6.6。更新前

PreUpdate 是最受限制的使用事件，因为它被称为 就在为实体内部调用更新语句之前 EntityManager#flush() 方法。 在此>事件中永远不允许更改已更新实体的关联，因为 Doctrine 无法保证在刷新操作的此时正确处理引用完整性。

这里描述了类似的情况preUpdate() 兄弟姐妹管理到树中：如何中断 ->persist() 递归？ https://stackoverflow.com/questions/30240230/preupdate-siblings-manage-into-tree-how-to-break-persist-recursion/30248488?noredirect=1#comment48612464_30248488

因此，您也可以采用类似的方式：创建自定义事件，创建自定义事件订阅者，您将在其中创建反向实体并在控制器操作处分派该事件订阅者。