Cakephp： 注意 8：undefined index： id 错误

问：

我得到未定义的索引：id [APP\controllers\merry_parents_controller.php，第 31 行]代码

debug($this->data['MerryParent']);
    echo 'id: '.$this->data['MerryParent']['id'];

 MerryParentsController::login() - APP\controllers\merry_parents_controller.php, line 31
 Dispatcher::_invoke() - CORE\cake\dispatcher.php, line 204
 Dispatcher::dispatch() - CORE\cake\dispatcher.php, line 171
 [main] - APP\webroot\index.php, line 83

我的代码：

merry_parents_controller.php

if ($this->Auth->user()){
            //debug($this->Auth->user());
            $this->data['MerryParent']=$this->Auth->user();
            debug($this->data['MerryParent']);
            echo 'id: '.$this->data['MerryParent']['id'];

对于 debug（$this->data['MerryParent']），记录显示正常：

Array
 (
  [MerryParent] => Array
    (
    [id] => 2
    [initial] => Ms
    [username] => hong
    [email] => [email protected]
    [password2] => hong7
    [landline] => 
    [mobile] => 293472389472
    [address] => dsaflkjasdlfk
    [state_id] => 5
    [city_id] => 62
    [postal_code] => 825729
    [created] => 2011-08-02 10:29:59
    [modified] => 2011-09-26 06:42:27
     )
)

但是当我尝试时 echo 'id： '.$this->data['MerryParent']['id'];

我收到通知 8：未定义的索引错误。我不知道问题出在哪里。有人可以帮我吗？