Confused about Spring-Data DDD repository pattern

Question

I don't know so much about DDD repository pattern but the implementation in Spring is confusion me.

public interface PersonRepository extends JpaRepository<Person, Long> { … }

As the interface extends JpaRepository (or MongoDBRepository...), if you change from one db to another, you have to change the interface as well.

For me an interface is there to provide some abstraction, but here it's not so much abstract...

Do you know why Spring-Data works like that?

Answer 1

You are right, an Interface is an abstraction about something that works equals for all implementing classes, from an outside point of view.

And that is exactly what happens here:

• JpaRepository is a common view of all your JPA Repositories (for all the different Entities), while MongoDBRepository is the same for all MongoDB Entities.

• But JpaRepository and MongoDBRepository have nothing in common, except the stuff that is defined in there common super Interfaces:

  • org.springframework.data.repository.PagingAndSortingRepository
  • org.springframework.data.repository.Repository

So for me it looks normal.

If you use the classes that implement your Repository then use PagingAndSortingRepository or Repository if you want to be able to switch from an JPA implementation to an Document based implementation (sorry but I can not imagine such a use case - anyway). And of course your Repository implementation should implement the correct interface (JpaRepository, MongoDBRepository) depending on what it is.