restful api响应JSON，model序列化问题 [ 2.0 版本 ]

用户表
id username pid
1 u1 0
2 u2 1
3 u3 2

User模型

控制器action

响应
Yii::$app->response->format = Response::FORMAT_JSON;

调用user/view?id=3响应的结果为：
{

id:3
username:'u3',
pid: 2
puser: {
	id:2
	username:'u2',
	pid: 1
	puser: {
		id:1
		username:'u1',
		pid: 0
		puser: {}
	}
}

}

调用user/index响应的结果为
[

{
	id:1
	username:'u1',
	pid: 0
	puser: []
},
{
	id:2
	username:'u2',
	pid: 1
	puser: {
		id:1
		username:'u1',
		pid: 0
		puser: []
	}
},
{
	id:3
	username:'u3',
	pid: 2
	puser: {
		id:2
		username:'u2',
		pid: 1
		puser: {
			id:1
			username:'u1',
			pid: 0
			puser: {}
		}
	}
}

]

请问万能的社区，有什么好的方案解决这问题吗？