Thanks for creating this ticket.

Unfortunately, as you mentioned, Elasticsearch 6 introduces a major breaking change in the fact that only one type is supported per index. This is a big problem for Hibernate Search as it is, because if we want to continue supporting the current features, it means we somehow have to:

• add a field to the Elasticsearch mapping to differenciate between types (which is easy)
• do the merging of multiple "elasticsearch mappings" into a single one that can be sent to Elasticsearch (which is not so easy)

I had started to experiment with this on one of my branches: GitHub: https://github.com/yrodiere/hibernate-search/tree/es6 but never went far because of this second item. Without it, a lots of our tests are failing and it's hard to tell if everything else works or not.

The current plan is to support Elasticsearch 6 in Hibernate Search 6 only, where we will prevent multiple entities to be mapped to the same index just as Elasticsearch does, thereby circumventing the main problem.

If you want to contribute support for Elasticsearch 6 in Hibernate Search 5.11, we would be glad to accept a PR, but it must pass the tests and not break any existing features, which will not be easy.