How to use @Transactional with Spring Data?

Issue

I just started working on a Spring-data, Hibernate, MySQL, JPA project. I switched to spring-data so that I wouldn't have to worry about creating queries by hand.

I noticed that the use of @Transactional isn't required when you're using spring-data since I also tried my queries without the annotation.

Is there a specific reason why I should/shouldn't be using the @Transactional annotation?

Works:

@Transactional
public List listStudentsBySchool(long id) {
    return repository.findByClasses_School_Id(id);
}

Also works:

public List listStudentsBySchool(long id) {
    return repository.findByClasses_School_Id(id);
}

Thanks in advance!

Solution

What is your question actually about? The usage of the @Repository annotation or @Transactional.

@Repository is not needed at all as the interface you declare will be backed by a proxy the Spring Data infrastructure creates and activates exception translation for anyway. So using this annotation on a Spring Data repository interface does not have any effect at all.

@Transactional - for the JPA module we have this annotation on the implementation class backing the proxy (SimpleJpaRepository). This is for two reasons: first, persisting and deleting objects requires a transaction in JPA. Thus we need to make sure a transaction is running, which we do by having the method annotated with @Transactional.

Reading methods like findAll() and findOne(…) are using @Transactional(readOnly = true) which is not strictly necessary but triggers a few optimizations in the transaction infrastructure (setting the FlushMode to MANUAL to let persistence providers potentially skip dirty checks when closing the EntityManager). Beyond that the flag is set on the JDBC Connection as well which causes further optimizations on that level.

Depending on what database you use it can omit table locks or even reject write operations you might trigger accidentally. Thus we recommend using @Transactional(readOnly = true) for query methods as well which you can easily achieve adding that annotation to you repository interface. Make sure you add a plain @Transactional to the manipulating methods you might have declared or re-decorated in that interface.

Answered By - Oliver Drotbohm