CakePHP:简单的Acl控制的应用程序-不允许我添加缺少的新用户组

我无法将用户添加到我的应用程序中，因为缺少group_id。。我遵循了本教程：http://book.cakephp.org/2.0/en/tutorials-and-examples/simple-acl-controlled-application/simple-acl-controlled-application.html组选择为空，我需要添加一个在之前创建的组

我的型号/用户.php

<?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'));
    /**      Validation rules        */
    public $validate = array(
        'username' => array(
            'notEmpty' => array(
                'rule' => array('notEmpty'),
                ),
        ),
        'password' => array(
            'notEmpty' => array(
                'rule' => array('notEmpty'),
                ),
        ),
        'group_id' => array(
            'numeric' => array(
                'rule' => array('numeric'),
                ),
        ),
    );
    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(
          $this->data['User']['password']
        );
        return true;
    }
    public function parentNode() {
        if (!$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));
        }
    }
}

我的型号/组.php

<?php
App::uses('AppModel', 'Model');
class Group extends AppModel {
    public $actsAs = array('Acl' => array('type' => 'requester'));
    public $validate = array(
        'name' => array(
            'notEmpty' => array(
                'rule' => array('notEmpty'),
            ),
        ),
    );
    public $hasMany = array(
        'User' => array(
            'className' => 'User',
            'foreignKey' => 'group_id',
            'dependent' => false,
            'conditions' => '',
            'fields' => '',
            'order' => '',
            'limit' => '',
            'offset' => '',
            'exclusive' => '',
            'finderQuery' => '',
            'counterQuery' => ''
        )
    );
    public function parentNode() {
        return null;
    }
}

我的视图/用户/add.ctp

<div class="users form">
<?php echo $this->Form->create('User'); ?>
    <fieldset>
        <legend><?php echo __('Add User'); ?></legend>
    <?php
        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>

和我的控制器/UsersController.php

<?php
App::uses('AppController', 'Controller');
class UsersController extends AppController {
public $components = array('Paginator');
public function index() {
        $this->User->recursive = 0;
        $this->set('users', $this->Paginator->paginate());
    }

    public function view($id = null) {
        if (!$this->User->exists($id)) {
            throw new NotFoundException(__('Invalid user'));
        }
        $options = array('conditions' => array('User.' . $this->User->primaryKey => $id));
        $this->set('user', $this->User->find('first', $options));
    }
    public function add() {
        if ($this->request->is('post')) {
            $this->User->create();
            if ($this->User->save($this->request->data)) {
                $this->Session->setFlash(__('The user has been saved.'));
                return $this->redirect(array('action' => 'index'));
            } else {
                $this->Session->setFlash(__('The user could not be saved. Please, try again.'));
            }
        }
    }
public function edit($id = null) {
        if (!$this->User->exists($id)) {
            throw new NotFoundException(__('Invalid user'));
        }
        if ($this->request->is(array('post', 'put'))) {
            if ($this->User->save($this->request->data)) {
                $this->Session->setFlash(__('The user has been saved.'));
                return $this->redirect(array('action' => 'index'));
            } else {
                $this->Session->setFlash(__('The user could not be saved. Please, try again.'));
            }
        } else {
            $options = array('conditions' => array('User.' . $this->User->primaryKey => $id));
            $this->request->data = $this->User->find('first', $options);
        }
    }
public function delete($id = null) {
        $this->User->id = $id;
        if (!$this->User->exists()) {
            throw new NotFoundException(__('Invalid user'));
        }
        $this->request->onlyAllow('post', 'delete');
        if ($this->User->delete()) {
            $this->Session->setFlash(__('The user has been deleted.'));
        } else {
            $this->Session->setFlash(__('The user could not be deleted. Please, try again.'));
        }
        return $this->redirect(array('action' => 'index'));
    }
    public function login() {
        if ($this->request->is('post')) {
            if ($this->Auth->login()) {
                return $this->redirect($this->Auth->redirect());
            }
            $this->Session->setFlash(__('Your username or password was incorrect.'));
        }
    }
    public function logout() {
        //Leave empty for now.
    }
    public function beforeFilter() {
        parent::beforeFilter();
        // For CakePHP 2.1 and up
        $this->Auth->allow();
    }
}