ClassAnalyzer.php

<?php

namespace App\Utils;

/**
 * Class ClassAnalyzer.
 */
class ClassAnalyzer
{
    /**
     * @param \ReflectionClass $class
     * @param string           $traitName
     *
     * @return bool
     */
    public static function hasTrait(\ReflectionClass $class, $traitName)
    {
        return \in_array($traitName, $class->getTraitNames(), true);
    }
}

services.yaml

services:
    App\Doctrine\EventSubscriber\TimestampableEntityEventSubscriber:
        tags:
            - { name: doctrine.event_subscriber }

TimestampableEntity.php

<?php

namespace App\Doctrine\Entity;

use Doctrine\ORM\Mapping as ORM;

/**
 * Trait TimestampableEntity.
 */
trait TimestampableEntity
{
    /**
     * @var \DateTime
     *
     * @ORM\Column(name="created_at", type="datetime")
     */
    protected $createdAt;

    /**
     * @var \DateTime
     *
     * @ORM\Column(name="updated_at", type="datetime")
     */
    protected $updatedAt;

    /**
     * @param \DateTime $createdAt
     *
     * @return $this
     */
    public function setCreatedAt(?\DateTime $createdAt)
    {
        $this->createdAt = $createdAt;

        return $this;
    }

    /**
     * @return \DateTime
     */
    public function getCreatedAt(): ?\DateTime
    {
        return $this->createdAt;
    }

    /**
     * @param \DateTime $updatedAt
     *
     * @return $this
     */
    public function setUpdatedAt(?\DateTime $updatedAt)
    {
        $this->updatedAt = $updatedAt;

        return $this;
    }

    /**
     * @return \DateTime
     */
    public function getUpdatedAt(): ?\DateTime
    {
        return $this->updatedAt;
    }
}

TimestampableEntityEventSubscriber.php

<?php

namespace App\Doctrine\EventSubscriber;

use App\Doctrine\Entity\TimestampableEntity;
use App\Utils\ClassAnalyzer;
use Doctrine\Common\Annotations\Reader;
use Doctrine\Common\EventSubscriber;
use Doctrine\ORM\EntityManagerInterface;
use Doctrine\ORM\Event\LifecycleEventArgs;
use Doctrine\ORM\Events;
use Doctrine\ORM\Mapping\ClassMetadata;

/**
 * Class TimestampableEntityEventSubscriber.
 */
class TimestampableEntityEventSubscriber implements EventSubscriber
{
    /**
     * @var Reader
     */
    protected $annotationReader;

    /**
     * TimestampableEntityEventSubscriber constructor.
     *
     * @param Reader $annotationReader
     */
    public function __construct(Reader $annotationReader)
    {
        $this->annotationReader = $annotationReader;
    }

    /**
     * @return array
     */
    public function getSubscribedEvents(): array
    {
        return [
            Events::prePersist,
            Events::preUpdate,
        ];
    }

    /**
     * @param LifecycleEventArgs $args
     *
     * @throws \Exception
     */
    public function prePersist(LifecycleEventArgs $args)
    {
        /** @var TimestampableEntity $entity */
        $entity = $args->getEntity();

        if (ClassAnalyzer::hasTrait($args->getEntityManager()->getClassMetadata(\get_class($entity))->reflClass, TimestampableEntity::class)) {
            $date = new \DateTime();

            $entity->setCreatedAt($date);
            $entity->setUpdatedAt($date);
        }
    }

    /**
     * @param LifecycleEventArgs $args
     *
     * @throws \Exception
     */
    public function preUpdate(LifecycleEventArgs $args)
    {
        /** @var TimestampableEntity $entity */
        $entity = $args->getEntity();

        /** @var EntityManagerInterface $entityManager */
        $entityManager = $args->getEntityManager();

        /** @var ClassMetadata $classMetadata */
        $classMetadata = $entityManager->getClassMetadata(\get_class($entity));

        if (ClassAnalyzer::hasTrait($classMetadata->reflClass, TimestampableEntity::class)) {
            $entity->setUpdatedAt(new \DateTime());

            $entityManager->getUnitOfWork()->recomputeSingleEntityChangeSet($classMetadata, $entity);
        }
    }
}