Should JPA entities and DDD entities be the same classes?

user_815741 0
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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 should JPA entities act just as a mechanism for a mapper (https://martinfowler.com/eaaCatalog/dataMapper.html) to load DDD entities from a database (and store them) and be kept outside the domain model?

Would it make a difference if database metadata were separated and stored externally (for example, in XML)? If such classes are entities, where is the boundary? I think classes generated from XSD (for example, with JAXB) or even from database with MyBatis Generator are not entities as understood in DDD.

mybatis-generator mybatis domain-driven-design jpa orm
4 Answers

After some more experience with JPA and microservices, I would say that I would most likely not separate them when using JPA, unless there's a reason that makes me do otherwise. On the other hand, entities in a single bounded context do not necessarily have to be only JPA entities. It's possible to have both entities mapped by JPA implementation and entities mapped from DTOs using other technologies (like JSON mappers) or manually.

user_8157410

I agree that both ways are possible. After programming some applications with DDD in mind, I find that this heuristic works well:

  • If you start from having an entity and not having JPA, it will probably be too hard to refactor an entity so that it can be used by ORM framework, so keep them separate
  • If you start from scratch, it is worth not distinguishing DDD entities from JPA entities
user_8157410
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