Spring Data JPA inserting instead of Update

By default Spring Data JPA inspects the identifier property of the given entity. If the identifier property is null, then the entity will be assumed as new, otherwise as not new. It's Id-Property inspection Reference

If you are using Spring JPA with EntityManager calling .merge() will update your entity and .persist() will insert.

@PersistenceContext
private EntityManager em;

@Override
@Transactional
public User save(User user) {

    if (user.getId() == null) {
        em.persist(user);
        return user;
    } else {
        return em.merge(user);
    }
}

There is no need to implement the Persistable interface.

I ran into this issue, tried to implement Persistable to no avail, and then looked into the Spring Data JPA source. I don't necessarily see this in your example code, but I have a @Version field in my entity. If there is a @Version field Spring Data will test that value to determine if the entity is new or not. If the @Version field is not a primitive and is null then the entity is considered new.

This threw me for a long time in my tests because I was not setting the version field in my representation but only on the persisted entity. I also don't see this documented in the otherwise helpful Spring Data docs (which is another issue...).

Hope that helps someone!