Doctrine ile created ve updated timestamp nasıl yaratılır

use Doctrine\ORM\Mapping as ORM;

/**
 * @ORM\Entity
 * @ORM\Table(name="league")
 * @ORM\HasLifecycleCallbacks
 */
class League
{
    /**
     * @ORM\Column(name="created_at", type="datetime", nullable=false)
     */
    protected $createdAt;

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

    /**
     * @ORM\PrePersist
     */
    public function onPrePersist()
    {
        $this->createdAt = new DateTime('now');
    }

    /**
     * @ORM\PreUpdate
     */
    public function onPreUpdate()
    {
        $this->updatedAt = new DateTime('now');
    }
}