Row was updated or deleted by another transaction (or unsaved-value mapping was incorrect)

Question

I have a java project that runs on a webserver. I always hit this exception.

I read some documentation, and found that pessimistic locking (or optimistic, but I read

Answer 1

This exception is probably caused by optimistic locking (or by a bug in your code). You're probably using it without knowing. And your pseudo-code (which should be replaced by real code to be able to diagnose the problem) is wrong. Hibernate saves all the modifications done to attached entities automatically. You shouldn't ever call update, merge or saveOrUpdate on an attached entity. Just do

Email email = session.get(emailId);
email.setSubject(subject);

No need to call update. Hibernate will flush the changes automatically before committing the transaction.