简单的Acl控制应用程序-不允许我添加新用户

我是CakePHP的新手，我正在尝试实现Simple Acl Controlled Application教程，我已经达到了尝试添加新用户和组的部分。。

我成功添加了组，但当我尝试添加新用户时，我会收到"该用户无法保存。请再试一次。"这是功能的一部分。

public function add() {
        if ($this->request->is('post')) {
            $this->User->create();
            if ($this->User->save($this->request->data)) {
                $this->Session->setFlash(__('The user has been saved'));
                $this->redirect(array('action' => 'index'));
            } else {
                $this->Session->setFlash(__('The user could not be saved. Please, try again.'));
            }
        }
    }

我注意到表单试图创建一个包含我创建的所有不同组的下拉框，但下拉框是空的，我创建了三个不同的组（管理员、响应者和志愿者）。

这是添加用户视图的副本。。

<div class="users form">
<?php echo $this->Form->create('User'); ?>
    <fieldset>
        <legend><?php echo __('Add User'); ?></legend>
    <?php
        echo $this->Form->input('id');
        echo $this->Form->input('username');
        echo $this->Form->input('password');
        echo $this->Form->input('group_id');
    ?>
    </fieldset>
<?php echo $this->Form->end(__('Submit')); ?>
</div>
<div class="actions">
    <h3><?php echo __('Actions'); ?></h3>
    <ul>
        <li><?php echo $this->Html->link(__('List Users'), array('action' => 'index')); ?></li>
    </ul>
</div>

型号按要求：

<?php
App::uses('AppModel', 'Model');
App::uses('AuthComponent', 'Controller/Component');
class User extends AppModel {
    public $belongsTo = array('Group');
    public $actsAs = array('Acl' => array('type' => 'requester'));
    public function parentNode() {
        if (!$this->id && empty($this->data)) {
            return null;
        }
        if (isset($this->data['User']['group_id'])) {
            $groupId = $this->data['User']['group_id'];
        } else {
            $groupId = $this->field('group_id');
        }
        if (!$groupId) {
            return null;
        } else {
            return array('Group' => array('id' => $groupId));
        }
    }
    public $primaryKey = 'id';
    public $validate = array(
        'id' => array(
            'numeric' => array(
                'rule' => array('numeric'),
            ),
        ),
        'username' => array(
            'notempty' => array(
                'rule' => array('notempty'),
            ),
        ),
        'password' => array(
            'notempty' => array(
                'rule' => array('notempty'),
            ),
        ),
        'group_id' => array(
            'numeric' => array(
                'rule' => array('numeric'),
            ),
        ),
    );
    //The Associations below have been created with all possible keys, those that are not needed can be removed
    //old belongs to
//    public $belongsTo = array(
//        'Group' => array(
//            'className' => 'Group',
//            'foreignKey' => 'group_id',
//            'conditions' => '',
//            'fields' => '',
//            'order' => ''
//        )
//    );
    public $hasMany = array(
        'Post' => array(
            'className' => 'Post',
            'foreignKey' => 'user_id',
            'dependent' => false,
            'conditions' => '',
            'fields' => '',
            'order' => '',
            'limit' => '',
            'offset' => '',
            'exclusive' => '',
            'finderQuery' => '',
            'counterQuery' => ''
        )
    );
    public function beforeSave($options = array()) {
        $this->data['User']['password'] = AuthComponent::password($this->data['User']['password']);
        return true;
    }
}

调试消息：

array(
    'User' => array(
        'password' => '*****',
        'id' => '',
        'username' => 'iwanjones'
    )
)

如有任何帮助，我们将不胜感激。感谢