How can i merge 2 different types

[sujoymondal87 (Sujoy Kumar Mondal)]

I need to merge two different 'types' (or two different 'indexes', even if this is a less preferred method) in ElasticSearch 5.6
This is the first type 'flag'
{
"_index": "flags",
"_type": "flag",
"_id": "1",
"_score": 1,
"_source": {
"title" : "Sad title is here"
"user_id" : 2
}
}
Here's the second 'user'
{
"_index": "flags",
"_type": "user",
"_id": "2",
"_score": 1,
"_source": {
"username" : "john doe"
}
}
The value of 'user_id' in type 'flag' is equal to the '_id' of the second type named 'user'
This is the result we're trying to get:
{
"_index": "flags",
"_type": "flag",
"_id": "1",
"_score": 1,
"_source": {
"title" : "Sad title is here"
"user_id" : 2,
"username" : 'john doe'
}
}
If it is possible to get the result by using different indeces instead of 'types', that is ok as well, but less preferred.

[dadoonet (David Pilato)]

Knowing that types are going to be removed I think it’s a good idea to do that.

This is something you need to solve IMO on the application side (ingestion side) or with an ETL.