Question

Is it correct that I never need to use EntityManager#merge(), as long as I only deal with attached managed entities? In other words, calling merge() on an attached managed entity has no effect?

Or are there circumstances where merging would serve a purpose? I find the name suggests that I could use it to deal with an OptimisticLockException… 🙂

Edit: In very simple terms, my understanding of a managed Entity is that modifications of its properties/fields get persisted to the DB at the end of the transaction.

Answer 1

The specification states that:

If X is a managed entity, it is ignored by the merge
operation, however, the merge operation is cascaded to entities
referenced by relationships from X if these relationships have been
annotated with the cascade element value cascade=MERGE or
cascade=ALL annotation.