How can I add an extra field to a nested document in ElasticSearch 5.6 when searching it

[sujoymondal87 (Sujoy Kumar Mondal)]

This is our nested document mapping:

{
 "properties" :{
  "user_id" :{"type": "integer"},  
  "images" : {
   "type": "nested",
   "properties": {
    "image_path": {"type": "string"}
     }
  }
 }
}

How it is indexed on ElasticSearch:

{
        "_index": "flags",
        "_type": "flag",
        "_id": "1",
        "_score": 1,
        "_source": {
          "user_id" : 2,
          "images" : [
                    {"image_path" : "123456.jpg"},
                    {"image_path" : "789101.jpg"},
             ]
        }
 }

We want to modify the path of "123456.jpg" and, depending of the specific API that was called, return a specific image path (folders name are static and known, we want to concat those with the picture name).

Desired result "upload/asd/123456.jpg":

 {
        "_index": "flags",
        "_type": "flag",
        "_id": "1",
        "_score": 1,
        "_source": {
          "user_id" : 2,
          "images" : [
                    {"image_path" : "upload/asd/123456.jpg"},
                    {"image_path" : "upload/qwe/789101.jpg"},
             ]
        }
 }

I have tried Script_fields but it is not working with nested documents.

[dadoonet (David Pilato)]

Why not doing that on the client side before injecting ?