我用renderJson(user)返回给客户端  user的内容为

{user_id:56, name:测试, id:6, add_time:2016-06-28 18:57:02.0, info:[{"date":"2016-05-10","temp":"32.5"},{"date":"2016-05-10","temp":"32.5"},{"date":"2016-05-10","temp":"32.5"},{"date":"2016-05-10","temp":"32.5"},{"date":"2016-05-10","temp":"32.5"}]}],其中user里面有一个二级主从 info。问题是renderJson(user)输出之后

变成了这样：

   {"result":[{"user_id":56,"name":"测试","id":6,"add_time":"2016-06-28 18:57:02","info":{}}],"stateCode":200,"message":""}  info 里面的信息为空了？这个是咋回事？