DAO

We configure our DAOs with annotations so that Spring Boot will manage them and their dependencies.

1. Mark the Impl class as javax.transaction.Transactional to have Spring automatically start a transaction for each DAO method and commit the transaction at the end of the method.

@Transactional
public class ActorDAOImpl implements ActorDAO {
  // ...
}

* An unchecked (runtime) exception will trigger a rollback.

1. Also above the class definition, add the @Service annotation.

2. Adding @Service will allow Spring Boot to create the DAO bean (found through component scanning) and inject it into the Controller using @Autowired.

@Transactional
@Service
public class ActorDAOImpl implements ActorDAO {
  // ...
}

1. Inject an EntityManager into a field using the @PersistenceContext annotation.

@Transactional
@Service
public class ActorDAOImpl implements ActorDAO {

  @PersistenceContext
  private EntityManager em;
  // ...
}

• You can now use this em field in your DAO methods to call find(), persist(), etc.

• This is a container-managed EntityManager, so you should NEVER call close() on it.

Drill

1. In com.example.bootmvc.data create an interface called FilmDAO that exposes a single method: Film findById(int id);.

2. Next create a class that implements the interface called FilmDAOJpaImpl.

3. Follow the steps listed above to configure the DAO implementation.

   • Instead of retrieving the EntityManager from the Persistence, declare an EntityManager as a field and annotate it with @PersistenceContext
4. Be sure to mark your FilmDAOJpaImpl with both @Transactional and @Service.
5. Add code into findById to retrieve a Film using the EntityManager find method.

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