authManager 权限问题，求助？ [ 新手入门 ]

代码：

$auth = Yii::app()->authManager;

//创建动作
$auth->createOperation('index','日志列表');
$auth->createOperation('view','查看日志');
$auth->createOperation('create','添加日志');
$auth->createOperation('update','更新日志');
$auth->createOperation('delete','添加列表');

//创建角色
$role = $auth->createRole('admin');
$role->addChild('index');
$role->addChild('view');
$role->addChild('create');
$role->addChild('update');
$role->addChild('delete');

//角色id=1的用户赋于admin角色
$auth->assign('admin', 20);

echo "<pre>\n";
var_export(Yii::app()->user->checkAccess('admin'));
echo "</pre>";
//exit;
exit

main.php

'authManager'=>array(
    'class'=>'CPhpAuthManager',
    //'authFile' => 'path'// only if necessary
),

输出总是false，请教下是为什么呢？