Merge an entity, change its id, merge again, cause “mapped to a primary key column in the database. Updates are not allowed” error

Question

I have a JPA program where EclipseLink is the Persistence provider. When I merge an user entity, change its ID, and try to merge the same user instance again, an error is thrown

Answer 1

The reason is that the Id may be inserted/defined - as you do in your second example, but not changed/updated - as you try in your first example. The JPA provider tries to reflect the change in the database and fails.

JPA 2 spec §2.4 says

The application must not change the value of the primary key. The behavior is undefined if this occurs.