Spring data repository and DAO Java Generics

Question

Reading about using Java Generics in DAO layer, I have a doubt applying this in spring data repositories. I mean, with spring data repositories, you have something like this:

  public interface OrderRepository extends CrudRepository<Order,OrderPK>{

  }

But if I have other 10 entities, I have to create 10 interfaces like the one above to execute CRUD operations and so on and I think this is not very scalable. Java Generics and DAO is about creating one interface and one implementation and reuse this for entities but with Spring Data repositories I have to create one interface for each entity so ...

Possible duplicate of [Using generics in Spring Data JPA repositories](https://stackoverflow.com/questions/19417670/using-generics-in-spring-data-jpa-repositories) — Jens Schauder, Oct 15 '18 at 07:25

score 3 · Accepted Answer · answered Mar 20 '17 at 10:17

You didn't really state a question, so I just add

Is this really true? And if so, why?

and answer it:

Yes, this is (almost) correct. Almost, because you should not create one repository per entity, but one repository per Aggregate Root. See http://static.olivergierke.de/lectures/ddd-and-spring/
Spring Data Repositories offer various features for which Spring Data needs to know, what entity it is dealing with. For example query methods need to know the properties of the entity, in order to convert the method name to JPA based query. So you have to pass in the information to Spring Data at some point and you also have to pass in the information, which entities should be considered Aggregate Roots. The way you do that, is by specifying the interface.

Do you really need that? Well if all you want is generic Crud functionality, you can get that straight out of the box with JPA. But if you want query methods, Pagination, simple native queries and much more Spring Data is a nice way to avoid lots of boiler-plate code.

(Please keep in mind that I'm biased)

Spring data repository and DAO Java Generics

1 Answers1