how to do unique validation, CodeIgniter2 + Doctrine2

[eluser]xjermx[/eluser]
Well I've found a solution. I'm not sure if its the best or most elegant, but it works.

Code:

$this->form_validation->set_rules('email', 'E-mail',
                 'required|valid_email|callback_email_check');

Code:

public function email_check($str)
{
$user = $this->doctrine->em->getRepository('Entities\User')->findOneBy(array('email' => $str));
    if (isset($user)) {
            $this->form_validation->set_message('email_check', 'This email address is already in use');
                    return FALSE;
    } else
    {
        return TRUE;
    }
}

Still open to anyone offering opinions on how this might be done better!