DAO

References

1. http://java.dzone.com/articles/jpa-implementation-patterns

Needs to DAO

Pro:

• unify using of EntityManager method of a team
• disallow certain operation / entity types
• theoretically may switch to another persistence system (but not realistically possible....)
• centralize all queries on a certain entity type
• no direct dependency on JPA
• type-safe
• possible to centralize debugging / profiling etc.
• one place to test database access code
• able to unit test business logic with mock DAO
• separate business logic with data access logic (some argue as con)

Against

• overhead
• cannot really hide JPA or under laying persistence mechanism very well

Competing with

• Active Record

Writing DAO

Option 1:

See Ref. 1, Vincent suggested:

• one generic DAO interface : public interface Dao<Key, Entity>
  • persist
  • remove
  • findById
• one abstract base JpaDao implementation : implements common methods, such as persist, etc.
• one sub-interface per entity : public interface OrderDao extends Dao<Integer, Order>
  • other specific methods
• one specific implementation per entity : public class JpaOrderDao extends JoaDao
• see http://java.dzone.com/articles/jpa-implementation-patterns