Question

I hava a basic Hibernate/JPA question. I want to find a best practice solution for saving entities. I have a List of Entities and many of them might be altered so I want to save them all at once.

I believe everything is pretty much standard. (Just example code for readability reasons)

Entity: Car

@Entity
public class Car implements Serializable {

    private static final long serialVersionUID = 1L;

    @Id
    private id;

    private String model;

    // .... Setter

    // .... Getter

}

Service Class: CarService

@Named
@Transactional
public class CarServiceImpl implements CarService {

    @PersistenceContext
    private EntityManager entityManager;

    @Override
    public List<Car> findAll() {
        TypedQuery<Car> q = entityManager.createQuery(
                "FROM Car", Car.class);
        return q.getResultList();
    }

    @Override
    public void saveEntity (Car car) {
        /* What exactly am I doing here? */
    }
}

Controller: CarEditController

@Named
public class CarEditController implements Serializable {

    private static final long serialVersionUID = 1L;

    @Inject
    private CarService carService;

    private List<Car> cars;

    public List<Car> getCars () {
        return carService.findAll();
    }

    public void setCars (List<Car> cars) {
        this.cars = cars;
    }

    public void btn_newClick() {
        Car newCar = new Car();
        car setModel("BMW");

        cars.add(newCar);
    }

    public void btn_saveClick() {
        for (Car car : cars) {
            carService.saveEntity(car);
        }
    }
}

I found quite a few ways of saving the entity. The obvious are entityManager.merge(car) for existing entities and entityManager.persist(car) for new ones. In theory thats easy but how do I know which entity is new?

The documentation suggests entityManager.flush(), which in theory updates all existing and inserts all new entities. It works but only if I fetch the entity with find().

The Question:

I want to fetch all entities in one step, add new ones and then save them all in one methode (btn_saveClick()). How is this task best accomplished?

Answer 1

Just check if the @Id is been set.

@Override
public void saveEntity (Car car) {
    if (car.getId() == null) {
        entityManager.persist(car);
    } else {
        entityManager.merge(car);
    }
}

More common approach, however, is to offer separate create() and update() service methods.