Mappers cause JPA entities to "detach" about buckpal HOT 1 CLOSED

Hi @yerundev ,

sorry for the late reply.

Yes, mapping JPA entities into domain entities will "undetach" them from the persistence session.

So, on the way back, when we're mapping the domain entities into JPA entities, we'll have to "re-attach" them. This usually works by just storing the ID of the entity in the domain model and, when mapping back into a JPA entity, using the same ID.

If a JPA entity has an ID, JPA providers should treat it as an existing entity and properly do updates.

I can't say why you get an EntityExistsException. JPA is obviously trying to do an insert instead of an update. There are cases (especially with *-to-many associations) that are more complicated to map. But it's possible. If you share some more code, maybe I can help.

A good thing is that the mapper is part of the persistence layer, where we want to tackle persistence-specific problems like this. This way we can keep problems like this out of the domain layer!

If we instead use JPA entities directly in the domain layer, we'll eventually have to solve persistence problems in the domain model, which always leads to tangled domain and persistence code.

from buckpal.