Provide a dedicated read-only repository interface [DATACMNS-1638]

[spring-projects-issues]

Vitor Carvalho opened DATACMNS-1638 and commented

Whenever a developer needs to create a read only repository, it has to extend the Repository interface and then add all the read methods from CrudRepository to it.

It would be useful to have a ReadRepository similar to CrudRepository with all the read only methods.

Optional<T> findById(ID id);

boolean existsById(ID id);

Iterable<T> findAll();

Iterable<T> findAllById(Iterable<ID> ids);

long count();

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No further details from DATACMNS-1638

[spring-projects-issues]

Oliver Drotbohm commented

This has been discussed a couple of times already and so far we've shied away from introducing additional repository base interfaces as the situation is far from trivial. Let me elaborate a bit.

The hierarchy of repository interfaces as non-trivial already

The repository hierarchy already contains quite a few interfaces for users to choose from:

– Repository<T, ID>
– CrudRepository<T, ID>
– PagingAndSortingRepository<T, ID>
– store-specific extensions

Providing even more of those complicates the picture significantly as we have to explain the tradeoffs for each interface we provide. The more we get opinionated about that the higher the chance that some of the interface almost meets a user's expectations but then again does not quite. We've had requests to remove the count() method as it's an expensive operation for some stores to implement. Or have a dedicated interface that prevents removal operations. So, where do we stop?

As a side note: interestingly we've seen your request from a different angle. Users asking for a repository not containing find operations other than findById(…) to make sure all but aggregate-by-id-lookups are declared using projection types, to essentially move towards a CQRS style application

Most applications craft their own base interface anyway

This is usually done for multiple purposes: one important one is to minimize the number of places with a fundamental Spring Data dependency in the codebase. Another one is aligning all repositories on a certain identifier type. A third one is slightly tweaking return values for common operations (e.g. returning Streamable instead of Iterable from the findAll… flavors available. If we introduce other base interfaces, chances are still high that users might (have to) do that as we cannot (and don't even necessarily want to) solve all those issues for them.

Changing the interface hierarchy is a breaking change

Introducing an interface in between Repository and CrudRepository breaks binary compatibility. I.e. all code currently compiled against e.g. CrudRepository.findById(…) would have to be recompiled. This naturally limits our ability to ship such a change to major revisions.

Also, we'd have to answer the question what interface PagingAndSortingRepository would extend? It only contains reading methods, which'd made it a natural candidate to extend ReadOnlyRepository. That however would break existing code as they'd all of a sudden miss the save(…) methods of CrudRepository. if we continue to let it extend CrudRepository it'd create some inconsistency of a repository interface primarily targeted at reading operations to include writing operations.

Concluding

I wonder how far we could get if we started with a mini library existing outside Spring Data that could try different arrangements based on Repository so that we can gain some experience in real world applications? As long as the methods stay signature compatible with the types we provide out of the box, the new interfaces should be usable without any friction

[spring-projects-issues]

Vitor Carvalho commented

Thanks for the explanation and actually I agree with everything you said.

Regarding this part "Introducing an interface in between Repository and CrudRepository", I understand that problem, and my suggestion was to have the new ReadOnly side by side with CrudRepository (both extending Repository), not between Repository and CrudRepository.

I didn't quite understand the concluding part though. Are you suggesting to have a separate library to "pack" all these commonly requested dedicated repositories? Like, having a ReadOnlyRepository, and a NoFindRepository, and a WithoutCountRepository, and others that are commonly requested?

[spring-projects-issues]

Oliver Drotbohm commented

Yes, a separate library would allow us to explore which subsets of repositories might make sense, alter those as feedback is coming in. Once we gained a bit more confidence, we can then move them over into Spring Data proper

[spring-projects-issues]

Vitor Carvalho commented

Looks like a good plan to me. How can we proceed?

[spring-projects-issues]

Oliver Drotbohm commented

Care to throw the interfaces you have into a repo at Github? Preferably accompanied by a few tests that make use of them to show that the CRUD methods still do what they're supposed to. We can then beat the drum for people to use them and see how it goes

[spring-projects-issues]

Vitor Carvalho commented

Sorry for the delayed response. Didn't had much free time unfortunately.
Here it is.
Also, here, I've created an example on how to use it with some tests using the Crud and ReadOnly, as you suggested.
-I was trying to use GitHub Actions to publish directly in GitHub Packages repository, but had some issues, and it stopped being published. Not sure why. Do you have any idea/suggestion that can help? Thanks- This is now fixed