如何插入自增长列啊？ [ 2.0 版本 ]

class Admin extends ActiveRecord{
    public $id;

    public $email;

    public $password;

    public $name;`

在控制器中：

public function actionAdd(){
    $admin = new Admin();
    $admin->name = 'dengdeng';
    $admin->email = 'dengdeng@123.com';
    $admin->password = '1234567';
    $admin->save();
};

会报错：

SQLSTATE[HY000]: General error: 1364 Field 'email' doesn't have a default value
The SQL being executed was: INSERT INTO `admin` (`id`) VALUES (NULL)

我的数据表结构是：id,email,name,password 其中id是自增长的