DboSource::expression PHP Method

    public function expression($expression)
    {
        $obj = new stdClass();
        $obj->type = 'expression';
        $obj->value = $expression;
        return $obj;
    }

 public function add()
 {
     //var_dump($this->request->data);
     $this->loadModel('User');
     $us = $this->User->find('all');
     //var_dump($us['0']);
     if (!empty($this->data)) {
         $this->loadModel('User');
         $this->User->create();
         //$this->request->data['User']['ip'] = $this->request->clientIp();
         $m = $this->request->data['User']['dob']['month'];
         $d = $this->request->data['User']['dob']['day'];
         $y = $this->request->data['User']['dob']['year'];
         $dob = $m . '-' . $d . '-' . $y;
         //$mem = $this->request->data['User']['member'];
         //var_dump($mem);
         $this->request->data['User']['dob'] = $dob;
         //$this->request->data['User']['mem'] = 'User';
         //$this->request->data['login_attempt']['login_times'] = 1;
         $this->request->data['User']['register_date'] = DboSource::expression('NOW()');
         if ($this->User->save($this->request->data)) {
             //echo "<div id='footer_a_link'>";
             $this->Session->setFlash('You are registered successfully. Please log in.');
             // $this->redirect(array('action' => 'login', 'controller' => 'Users'));
         } else {
             $this->Session->setFlash('Not Registered');
         }
     }
 }