How does Spring Data JPA differ from Hibernate for large projects?

So, spring-data does some extra magic that helps with complex queries. It is strange at first and you totally skip it in the docs but it is really powerful and useful.

It involves creating a custom Repository and a custom `RepositoryImpl' and telling Spring where to find it. Here is an example:

Configuration class - point to your still-needed xml config with annotation pointing to your repositories package (it looks for *Impl classes automatically now):

@Configuration
@EnableJpaRepositories(basePackages = {"com.examples.repositories"})
@EnableTransactionManagement
public class MyConfiguration {
}

jpa-repositories.xml - tell Spring where to find your repositories. Also tell Spring to look for custom repositories with the CustomImpl file name:

MyObjectRepository - this is where you can put annotated and unannotated query methods. Note how this repository interface extends the Custom one:

@Transactional
public interface MyObjectRepository extends JpaRepository<MyObject, Integer>, MyObjectRepositoryCustom {

    List<MyObject> findByName(String name);

    @Query("select * from my_object where name = ?0 or middle_name = ?0")
    List<MyObject> findByFirstNameOrMiddleName(String name);
}

MyObjectRepositoryCustom - repository methods that are more complex and cannot be handled with a simple query or an annotation:

public interface MyObjectRepositoryCustom {

    List<MyObject> findByNameWithWeirdOrdering(String name);
}

MyObjectRepositoryCustomImpl - where you actually implement those methods with an autowired EntityManager:

public class MyObjectRepositoryCustomImpl implements MyObjectRepositoryCustom {

    @Autowired
    private EntityManager entityManager;

    public final List<MyObject> findByNameWithWeirdOrdering(String name) {
        Query query = query(where("name").is(name));
        query.sort().on("whatever", Order.ASC);
        return entityManager.find(query, MyObject.class);
    }
}

Amazingly, this all comes together and methods from both interfaces (and the CRUD interface, you implement) all show up when you do:

myObjectRepository.

You will see:

myObjectRepository.save()
myObjectRepository.findAll()
myObjectRepository.findByName()
myObjectRepository.findByFirstNameOrMiddleName()
myObjectRepository.findByNameWithWeirdOrdering()

It really does work. And you get one interface for querying. spring-data really is ready for a large application. And the more queries you can push into simple or annotation only the better off you are.

All of this is documented at the Spring Data Jpa site.

Good luck.

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I've used Spring Data JPA in small and large projects with simple query demands. The main advantage is from not even having to use the @Query annotation. There is nothing in Spring Data that prevents you from using it in large projects and the recent QueryDSLsupport might help you. This is an example of using QueryDSL to target Hibernate.

If you foresee complex queries and you feel comfortable using Hibernate objects without JPA I think an alternative combination could be to have the simple Spring Data Repositorys next to complex Hibernate-based ones with the specific methods you might need. It might be less cumbersome that twisting a Hibernate implementation into Spring Data JPA structure.

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Spring JPA will provide you a lot of abstraction from writing SQL and even some HQL using query method declaration. Spring JPA shines with its query generation but when you want a purely hibernate solution you can customize as needed as spring JPA is still based on hibernate. Check the docs http://static.springsource.org/spring-data/data-jpa/docs/current/reference/html for more info.

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