Why use returned instance after save() on Spring Data JPA Repository?

Question

Here is the code:

@Repository
public interface AccountRepository extends JpaRepository {}

JpaRepository from

Answer 1

You missed the second part: if the entity isn't new, merge is called. merge copies the state of its argument into the attached entity with the same ID, and returns the attached entity. If the entity isn't new, and you don't use the returned entity, you'll make modifications to a detached entity.