Symfony Circular Reference Exception for Doctrine onFlush Event Listener Service

Question

I have created a service for a Doctrine onFlush event listener. In this listener I would like to reference a common function I have in another service to check the entity's shortcut path. That other service uses the entity manager to do this, so the service definition for that other service injects the doctrine entity manager as a constructor argument. But if I include that other service in my main onFlush event listener, I get a nasty error about circular references.

I could make this entity_helper service accept the Entity Manager in a set function setEntityManager($entityManager). But that means whenever I use this entity_helper service anywhere else, I have to always pass in the EntityManager. Maybe that's okay, but is that the only solution here? Is there something wrong with my logic/understanding to begin with? (I am new to Symfony so I'm frequently wrong).

Exhibit A: Nasty Error

Fatal error: Uncaught exception 'Symfony\Component\DependencyInjection\Exception\ServiceCircularReferenceException' with message 'Circular reference detected for service "doctrine.dbal.cms_connection", path: "doctrine.dbal.cms_connection".' in /var/www/core/cms/vendor/symfony/symfony/src/Symfony/Component/DependencyInjection/Dumper/PhpDumper.php:456 Stack trace: #0 /var/www/core/cms/vendor/symfony/symfony/src/Symfony/Component/DependencyInjection/Dumper/PhpDumper.php(604): Symfony\Component\DependencyInjection\Dumper\PhpDumper->addServiceInlinedDefinitionsSetup('doctrine.dbal.c...', Object(Symfony\Component\DependencyInjection\Definition)) #1 /var/www/core/cms/vendor/symfony/symfony/src/Symfony/Component/DependencyInjection/Dumper/PhpDumper.php(630): Symfony\Component\DependencyInjection\Dumper\PhpDumper->addService('doctrine.dbal.c...', Object(Symfony\Component\DependencyInjection\Definition)) #2 /var/www/core/cms/vendor/symfony/symfony/src/Symfony/Component/DependencyInjection/Dumper/PhpDumper.php(117): Symfony\Componen in /var/www/core/cms/vendor/symfony/symfony/src/Symfony/Component/DependencyInjection/Dumper/PhpDumper.php on line 456

Services.yml

# This is the helper class for all entities
gutensite_cms.entity_helper:
    class: Gutensite\CmsBundle\Service\EntityHelper
    # This causes the Circular Reference Error when this service is included in Event Listener
    arguments: [ "@doctrine.orm.cms_entity_manager" ]
    # Passing via a setter injection also causes the same error.
    #calls:
    #    - [setEntityManager, ['@doctrine.orm.cms_entity_manager']]


# An event listener for any entity that is Versionable
gutensite_cms.listener.is_versionable:
    class: Gutensite\CmsBundle\EventListener\IsVersionableListener
    #only pass in the services we need
    arguments: [ "@gutensite_cms.entity_helper" ]
    tags:
        - { name: doctrine.event_listener, event: onFlush }

Gutensite\CmsBundle\Service\EntityHelper

namespace Gutensite\CmsBundle\Service;

use Doctrine\ORM\EntityManager;

class EntityHelper {

    /**
     * @var $em EntityManager
     */
    private $em;

    public function __construct(EntityManager $entityManager) {
        $this->em = $entityManager;
    }

    /**
     * Get the bundle shortcut path for an entity based on it's namespace.
     *
     * As an example, if your entity is Gutensite\CmsBundle\Entity\View\ViewVersion the function will return
     * GutensiteCmsBundle:View\ViewVersion
     *
     * @param $entity
     * @return string
     */
    public function getEntityBundleShortcut($entity) {
        // wrap get_class() in the entityManager metadata function to avoid returning cached proxy class
        $path = explode('\Entity\\', $this->em->getClassMetadata(get_class($entity))->getName());
        return str_replace('\\', '', $path[0]).':'.$path[1];
    }

}

Gutensite\CmsBundle\EventListener\IsVersionableListener

namespace Gutensite\CmsBundle\EventListener;

use Doctrine\ORM\Event\OnFlushEventArgs;
use Gutensite\CmsBundle\Service\EntityHelper;


/**
 * Class IsVersionableListener
 * @package Gutensite\CmsBundle\EventListener
 */
class IsVersionableListener
{

    /*
    private $entityHelper;

    public function __construct(EntityHelper $entityHelper) {
        $this->entityHelper = $entityHelper;
    }
    */

    public function onFlush(OnFlushEventArgs $eventArgs)
    {

        // This never is excecuted because of the error
        print('ON FLUSH EVENT EXECUTED');
        exit;

        $em = $eventArgs->getEntityManager();
        $uow = $em->getUnitOfWork();
        $updatedEntities = $uow->getScheduledEntityUpdates();

        foreach($updatedEntities AS $entity) {

            // This is generic listener for all entities that have an isVersionable method (e.g. ViewVersion)
            // TODO: at the moment, we only want to do the following code for the viewVersion entity

            if (method_exists($entity, 'isVersionable') && $entity->isVersionable()) {

                // Get the Correct Repo for this entity
                $entityShortcut = $this->entityHelper->getEntityBundleShortcut($entity);
                $repo = $em->getRepository($entityShortcut);

                // If the repo for this entity has an onFlush method, use it.
                // This allows us to keep the functionality in the entity repo
                if(method_exists($repo, 'onFlush')) {
                    $repo->onFlush($em, $entity);
                }

            }
        }
    }
}

Answer 1

The basic solution to this (as I indicated) is to remove the construct or setter injection of the EntityManager from the service definition (and the service class). Instead you have to pass the EntityManager into the function that needs it. This prevents the circular reference.

I opted for this instead of a creating a setEntityManager because it seems clunky to have to set that on the EntityHelper service, before calling the function. It seems better to just pass it to the functions that need it directly.

Here are the changes:

Services.yml

# This is the helper class for all entities
gutensite_cms.entity_helper:
    class: Gutensite\CmsBundle\Service\EntityHelper
    # Do NOT pass in EntityManager via constructor or injector, because it causes a Circular Reference Error when this service is included in Event Listener


# An event listener for any entity that is Versionable
gutensite_cms.listener.is_versionable:
    class: Gutensite\CmsBundle\EventListener\IsVersionableListener
    #only pass in the services we need
    arguments: [ "@gutensite_cms.entity_helper" ]
    tags:
        - { name: doctrine.event_listener, event: onFlush }

Gutensite\CmsBundle\Service\EntityHelper

namespace Gutensite\CmsBundle\Service;

use Doctrine\ORM\EntityManager;

class EntityHelper {


    /**
     * Get the bundle shortcut path for an entity based on it's namespace.
     *
     * As an example, if your entity is Gutensite\CmsBundle\Entity\View\ViewVersion the function will return
     * GutensiteCmsBundle:View\ViewVersion
     *
     * @param $entity
     * @return string
     */
    public function getEntityBundleShortcut(EventManager $eventManager, $entity) {
        // wrap get_class() in the entityManager metadata function to avoid returning cached proxy class
        $path = explode('\Entity\\', $eventManager->getClassMetadata(get_class($entity))->getName());
        return str_replace('\\', '', $path[0]).':'.$path[1];
    }

}

Gutensite\CmsBundle\EventListener\IsVersionableListener

namespace Gutensite\CmsBundle\EventListener;

use Doctrine\ORM\Event\OnFlushEventArgs;
use Gutensite\CmsBundle\Service\EntityHelper;


/**
 * Class IsVersionableListener
 * @package Gutensite\CmsBundle\EventListener
 */
class IsVersionableListener
{

    /*
    private $entityHelper;

    public function __construct(EntityHelper $entityHelper) {
        $this->entityHelper = $entityHelper;
    }
    */

    public function onFlush(OnFlushEventArgs $eventArgs)
    {

        $em = $eventArgs->getEntityManager();
        $uow = $em->getUnitOfWork();
        $updatedEntities = $uow->getScheduledEntityUpdates();

        foreach($updatedEntities AS $entity) {

            // This is generic listener for all entities that have an isVersionable method (e.g. ViewVersion)
            // TODO: at the moment, we only want to do the following code for the viewVersion entity

            if (method_exists($entity, 'isVersionable') && $entity->isVersionable()) {

                // Get the Correct Repo for this entity
                $entityShortcut = $this->entityHelper->getEntityBundleShortcut($em, $entity);
                $repo = $em->getRepository($entityShortcut);

                // If the repo for this entity has an onFlush method, use it.
                // This allows us to keep the functionality in the entity repo
                if(method_exists($repo, 'onFlush')) {
                    $repo->onFlush($em, $entity);
                }

            }
        }
    }
}