Retrive parent data inside child doc from index

[Sagar_Darekar]

We have a requirement that we need to retrieve parent fields inside the child document.
Actually we have a mapping for the index as below:

{
    "mappings": {
        "properties": {
            "relation_type": {
                "eager_global_ordinals": true,
                "type": "join",
                "relations": {
                    "user": "forum"
                }
            }
        }
    }
}

Parent and child relationship is maintained between user and forum. I need to retrieve the user(parents) data inside the forum(child).
For example - User doc

{
  "hn": "handle",
  "iu": "user-image-url",
  "uId": "user-id",
  "relation_type": {
    "name": "user"
  }
}

And forum doc -

{
    "uId": "userId",
    "pId": "postId",
    "relation_type": {
      "name": "forum",
      "parent": "userID"
    }
}

I need to write a query such that it retrieves user data(user image) inside child data. For example - below is the result I wanted in the forum(child) query result with iu(image URL) from the user.

{
    "uId": "userId",
    "pId": "postId",
     "iu": "user image" //user image from user doc
    "relation_type": {
      "name": "forum",
      "parent": "userID"
    }
}

I have posted the same on the stack overflow forum. - https://stackoverflow.com/questions/62468004/retrive-parent-data-embeded-in-child-doc-from-elastic-search-index

Need to know if it is possible or not, if yes then how?