Should JPA entities and DDD entities be the same classes?

Question

There are classes that are entities according to DDD, and there are classes that have @javax.persistence.Entity annotation. Should they be the same classes? Or

Answer 1

Your JPA entities should be the domain entities. Why? Your domain entities should express some strong constraints, e.g. by

• Having parameterized constructors
• Not exposing all setters
• Do validation on write operations

If possible, a domain entity should always remain a valid business entity. By introducing some kind of mapper, you introduce a possibility to automagically write arbitrary stuff into your domain entities, which basically renders your constraints useless.

The other option would be enforcing the same constraints on JPA and domain entities which introduces redundancy.

Your best bet is keeping your JPA entities as ORM-agnostic as possible. Using Hibernate, this can be done using a configurating class or XML file. But I am no Java EE/JPA guy, so it's hard for me to give a good implementation advice.