cakephp,如何在两个表中保存数据？

class User extends AppModel {
    public $hasMany = array('Post');
}

class Post extends AppModel {
    public $belongsTo = array('User');
}

class UsersController extends AppController {
    public function add() {
        if ($this->request->is('post')) {
            $this->User->create();
            $userData = array(
                'username' => 'JohnDoe',
                'email' => 'johndoe@example.com',
                'password' => 'password123'
            );
            $this->User->save($userData);
            $userId = $this->User->getLastInsertId();

            $postData = array(
                'title' => 'My first post',
                'content' => 'This is my first post content.',
                'user_id' => $userId
            );
            $this->User->Post->save($postData);
        }
    }
}