[STORE] Warn that the ActiveRecord persistence pattern is deprecated

[estolfo]

No description provided.

[holidayworking]

Why the ActiveRecord Pattern is deprecated?

[karmi]

Hi @holidayworking, it's a consequence of multiple forces we have seen both when working in the codebase and in the practical usage, our own and in the wild.

As much as the ActiveRecord pattern is attractive for a quick start with persisting objects, particularly in Rails-based applications, we do see "impedance mismatches" between a storage like Elasticsearch and the ActiveRecord semantics, ranging from technical issues like consistency guarantees to conceptual ones like too tight coupling of business logic with the persistence details.

Particularly in our own internal use of the elasticsearch-persistence Rubygem, we have observed a much cleaner separation of concerns when using the Repository pattern. That particular persistence pattern is much more flexible in a larger codebase, while still being quite simple to use — in the end, you initialize a repository and then pass objects to it:

repository = Elasticsearch::Persistence::Repository.new
repository.save(my_object)

We are quite keen to explore and extend this pattern much more in the elasticsearch-persistence Rubygem, and we plan to refactor the example to provide thorough, code-based instructions for people how to migrate between this patterns.

Please note that this applies to the persistence library only: the integration with Ruby models (ActiveModel/ActiveRecord) doesn't go away, quite the opposite — we do plan to start fixing the outstanding issues on that front.