[FLOW3-general] Storing default values or properties into database

[Nkongme]

Hi guys,

I would like to use the model below to automatically store a timestamp 
into the database when a user object is created and persisted. When I 
use the code below, the property/field "registrationdate" is always 
stored with the value 0000-00-00 00:00:00 and not the actual date. What 
am I doing wrong?

use Doctrine\ORM\Mapping as ORM;
use TYPO3\FLOW3\Annotations as FLOW3;

/**
  * A User
  *
  * @FLOW3\Scope prototype
  * @FLOW3\Entity
  */
class User {

	/**
	 * The name
	 * @var string
	 */
	protected $name;

     /**
      * @var \DateTime
      * @ORM\Column(type="datetime")
      */
     protected $registrationdate;

     /**
      * Constructs this user
      */
     public function __construct() {
         $this->registrationdate = new \DateTime();
     }	
	
     /**
	 * Get the User's name
	 *
	 * @return string The User's name
	 */
	public function getName() {
		return $this->name;
	}

	/**
	 * Sets this User's name
	 *
	 * @param string $name The User's name
	 * @return void
	 */
	public function setName($name) {
		$this->name = $name;
	}

}

I would appreciate any suggestions. Thanks!
Ed