Spring JPA repository: prevent update on save

When using the default configuration, and using CrudRepository#save() or JpaRepository#save() it will delegate to the EntityManager to use either persists() if it is a new entity, or merge() if it is not.

The strategy followed to detect the entity state, new or not, to use the appropiate method, when using the default configuration is as follows:

• By default, a Property-ID inspection is performed, if it is null, then it is a new entity, otherwise is not.
• If the entity implements Persistable the detection will be delegated to the isNew() method implemented by the entity.
• There is a 3rd option, implementing EntityInformation, but further customizations are needed.

source

So in your case, as you are using the username as ID, and it isn't null, the Repository call ends up delegating to EntityManager.merge() instead of persist(). So there are two possible solutions:

• use a diferent ID property, set it to null, and use any auto-generation method, or
• make User implement Persistable and use the isNew() method, to determine if it is a new entity or not.

---

If for some reason, you don't want to modify your entities, you can also change the behaviour modifying the flush mode configuration. By default, in spring data jpa, hibernate flush mode is set to AUTO. What you want to do is to change it to COMMIT, and the property to change it is org.hibernate.flushMode. You can modify this configuration by overriding a EntityManagerFactoryBean in a @Configuration class.

---

And if you don't want to mess the configuration of the EntityManager, you can use the JpaRepository#flush() or JpaRepository#saveAndFlush() methods, to commit the pending changes to the database.