[doctrine-user] Auto create date - annoation - Codeigniter 2 and Doctrine 2

insert.php

<?php
$worker = new models\Workers();
$worker->setEmail($data['email']);
$this->em->persist($worker);
$this->em->flush();

Workers.php

<?php
namespace models;

/**
 * @Entity
 * @Table(name="workers")
 * @HasLifecycleCallback
 */
class Workers {
   /**
    * @Id
    * @Column(type="integer", nullable=false)
    * @GeneratedValue(strategy="AUTO")
    */
   protected $id;

   /**
    * @Column(type="string", length=255, unique=true, nullable=false)
    */
   protected $email;

   /**
    * @var datetime $created_on
    *
    * @gedmo:Timestampable(on="create")
    * @Column(type="datetime")
    */
   protected $created_on;


   /** @PrePersist */
   function onPrePersist()
   {
       $this->created_on = new \DateTime();
   }

   /* Setters & Getters */
   public function setEmail($email){ $this->email = $email; }
   public function getEmail(){ return $this->email; }
}