[watwut]

The "session.load(Person.class, 2)" thing is not done normally. It is not even part of JPA. It is hibernate only feature.

So in all project I have seen, calling setter did not changed database.

> Do you mean that people normally call update or merge to persist an Entity?

Yes, people normally call update and merge to persist an entity.

[alserio]

People normally do that when they do not have to do that.

  Dog rex = em.find(Dog.class,"rex"); // 1
  rex.setAge(2); // 2
  // other query // 3

At 3 the update is flushed on the underlying db. This is pure JPA. Calling merge is forcing an useless query before the update. Also, merge returns the managed entity.