Introduce `ValidatingEntityCallback` and deprecate `ValidatingMongoEventListener`

[rfelgent]

Hello,

I would like to contribute a ValidatingEntityCallback (in addition to the ValidatingMongoEventListener) to the code base.

The ValidatingMongoEventListener is not suitable for me due to the design nature of EventListener and EntityCallback. I prefer EntityCallback

IMHO the ValidatingMongoEventListener should (even) be marked as deprecated, because

• the EntityCallbacks are recommended by the Spring docs and
• EventListener are by design triggered/executed before any EntityCallback. This can lead to undesired behaviour difficult to track down by a developer, e.g. validation of entity happens before the entity in request is manipulated by any EntityCallback

If the maintainers/team accept my enhancement proposal, I can make a pull request.

[mp911de]

Looking at our Bean Validation integration, MongoDB is the only module that ships with a Bean Validation integration. It is an extremely thin layer component that mandates a dependency on Bean Validation. ValidatingMongoEventListener is registered by our config when Bean Validation is on the classpath.

For the upcoming major 5.0 version of Spring Data MongoDB, we could switch from registering a listerner into registering an EntityCallback. Let me take this ticket to the team to see what they think about it.

[mp911de]

After talking with the team, we'd happily accept a pull request.

[rfelgent]

Cool @mp911de!

One quick question regarding the implementation:

Do you prefer a dedicated "callback-entity" class (not exist) and a dedicated "event-listener" class (already exisists) or is one validator class impementing both interfaces sufficent?

If you prefer the "dedicated" classes option, I tend to put the validation logic in one abstract/base class and let the other classes extend from it.

What do you think ?

[rfelgent]

Answering the question myself: due to different @Order requirements for ValidatingEntityCallback and ValidatingMongoEventListener I have to design two dedicated classes.

here is the PR