Using a combined field as id mapping in ElasticSearch

Question

From this question I can see that it is possible Use existing field as id in elasticsearch

My question is, if can do similar thing but concatenating fields.

Answer 1

No you can't, you can only make the _id point to a field that's within the document, using the dot notation as well if needed (e.g. level1,level2.id).

I'd suggest to have a field that contains the whole id in your documents, or even better to take the id out and provide it in the url, as configuring a path causes the document to be parsed when not needed.