求解：Call to a member function [ 未指定版本 ]

Call to a member function getDb() on a non-object in framework/db/ar/CActiveRecord.php

代码如下：

$yii='./framework/yii.php';
require_once($yii);

class User extends CActiveRecord{
	var $primaryKey = 'code';
	
	public static function model($className=__CLASS__)
	{
		return parent::model($className);
	}
	public function tableName()
	{
		return 'user_tb';
	}
}


$user = new User();

$user->user_name = "test";
$user->pwd = "test";

$user->save();