public function actionCreate()
{
    $model=new User;

    // Uncomment the following line if AJAX validation is needed
    // $this->performAjaxValidation($model);

    if(isset($_POST['User']))
    {
        $_POST['User']['salt']=$model->$_POST['User']['password'];
        $_POST['User']['password']=md5($_POST['User']['salt'] . $_POST['User']['password']);
        $model->attributes=$_POST['User'];
        if($model->save())
            $this->redirect(array('view','id'=>$model->id));
    }

    $this->render('create',array(
        'model'=>$model,
    ));
}

这样写正确吗？

$_POST['User']['salt']=$model->$_POST['User']['password'];
$_POST['User']['password']=md5($_POST['User']['salt'] . $_POST['User']['password']);

这两句起什么作用啊？