Symfony2: Update the slug of a product with ID-TITLE (postPersist)

Product.php

<?php
// src/Aki/MyBundle/Entity/Product.php

/**
 * [...]
 * @ORM\HasLifecycleCallbacks()
 */
class Product
{
 [...]
 

service.yml

services:
    aki.slug:
        class: Aki\MyBundle\Listener\SlugUpdate
        tags:
            - { name: doctrine.event_listener, event: postPersist }

SlugUpdate.php

 <?php
// src/Aki/MyBundle/Listener/SlugUpdate.php

namespace Aki\MyBundle\Listener;
 
use Aki\MyBundle\Entity\Product;
use Doctrine\ORM\Event\LifecycleEventArgs;
 
class SlugUpdate
{
    public function postPersist(LifecycleEventArgs $args)
    {
        $entity = $args->getEntity();
        $em = $args->getEntityManager();
 
        if ($entity instanceof Product) {
            $entity->setSlug(null);
 
            $em->persist($entity);
            $em->flush();
        }
    }
}