cakeCakephp，未显示验证消息

我无法在CakePHP控制器类中捕获并显示验证错误。我有这个型号：

public $validate = array(
    'username' => array(
        'notEmpty' => array(
            'rule' => array('notEmpty'),
            'message' => 'Your custom message here',
            'allowEmpty' => false,
            'required' => true,
            //'last' => false, // Stop validation after this rule
            //'on' => 'create', // Limit validation to 'create' or 'update' operations
        ),
        'alphaNumeric' => array(
            'rule' => array('alphaNumeric'),
            'message' => 'Your custom message here',
            //'allowEmpty' => false,
            //'required' => false,
            //'last' => false, // Stop validation after this rule
            //'on' => 'create', // Limit validation to 'create' or 'update' operations
        ),
        'maxLength' => array(
            'rule' => array('maxLength', 50),
            'message' => 'Your custom message here',
            //'allowEmpty' => false,
            //'required' => false,
            //'last' => false, // Stop validation after this rule
            //'on' => 'create', // Limit validation to 'create' or 'update' operations
        ),
    ));

这就是我在将一个新元素保存到数组中时，试图将验证消息捕获到控制器中的方式：

public function add() {
    if ($this->request->is('post')) {
        $this->Admin->set($this->request->data);
        //$this->Admin->create();
        if ($this->Admin->validates()) {
            // it validated logic
            if ($this->Admin->save($this->request->data)) {
                $this->Session->setFlash(__('The admin has been saved.'));
                return $this->redirect(array('action' => 'index'));
            } else {
                $this->Session->setFlash(__('The admin could not be saved. Please, try again.'));
            }
        } else {
            // didn't validate logic
            $errors = $this->Admin->validationErrors;
            debug($errors);
        }
    }
}

但它不起作用。如果我传递了一个空字段，那么add.ctp页面中会显示一个带有默认消息的警报。如果我插入一个重复，则不会显示任何消息。