PostEntityListener.php

<?php

namespace App\Doctrine\EntityListener;

use Doctrine\ORM\EntityManagerInterface;
use Doctrine\ORM\Event\OnFlushEventArgs;
use App\Entity\Post;

class PostEntityListener {

    /**
     * @inheritDoc
     * @param OnFlushEventArgs $event
     * @return void
     */
    public function onFlush(OnFlushEventArgs $event) {
        $em = $event->getEntityManager();
        $uow = $em->getUnitOfWork();
        foreach ($uow->getScheduledCollectionUpdates() as $collection) {
            $entity = $collection->getOwner();
            if ($entity instanceof Post) {
             // next step   
            }
        }
    }
}