如何对其他字段中存在的字段进行排序

Question

我需要按字段first_name排序。

{  
 "_index":"data1",
 "_type":"data1",
 "_id":"190204051110",
 "_score":1,
 "_source":{  
  "hello_info":{  
     "first_name":"abc"
  },
  "created":"2019-02-04T05:11:10.058470",
  "modified":"2019-02-04T11:10:47.122065"
 }
}