Retrieving an entity via the getReference
method doesn’t involve any database access. If one or more fields (excluding the ID field) are updated and then persist
is invoked, will Hibernate retrieve the entity from the database before persisting it? Or does it persist the updated fields with just one SQL query, leaving the other fields unchanged?
Code example:
User user = entityManager.getReference(User.class, id);
user.setUsername(username);
entityManager.persist(user);