Are persistence annotations in domain objects a bad practice?

Question

I realize that persistence frameworks such as Morphia and Hibernate rely on annotations on domain objects to do their magic. At some level, it seems to me that this is insertin

Answer 1

I've recently worked on a reasonably complex system with had a separate persistence layer, and it was a huge pain in the ass and very bad for maintainability. You're basically looking at a conflict between the principles of YAGNI and Single Responsibility. In my opinion, YAGNI is the more important one (alas, also the more frequently ignored one).

I'd say in the vast majority of cases, it's much better to persist domain objects directly if you're using an ORM, unless you have concrete requirements that force the persistence entities to be structured differently (if they have exactly the same structure, there is no reason to separate them except ivory tower arguments).

To be sure: always do the actual persistence stuff (calling ORM functions) in a separate service/DAO layer! That way, it's easy to introduce a persistence layer later if you find that you need it.