How to enable LockModeType.PESSIMISTIC_WRITE when looking up entities with Spring Data JPA?

Question

How can I achieve the equivalent of this code:

tx.begin();
Widget w = em.find(Widget.class, 1L, LockModeType.PESSIMISTIC_WRITE);
w.decrementBy(4);
em.flush();
tx.commit();

... but using Spring and Spring-Data-JPA annotations?

The basis of my existing code is:

@Service
@Transactional(readOnly = true)
public class WidgetServiceImpl implements WidgetService
{
  /** The spring-data widget repository which extends CrudRepository<Widget, Long>. */
  @Autowired
  private WidgetRepository repo;

  @Transactional(readOnly = false)
  public void updateWidgetStock(Long id, int count)
  {
    Widget w = this.repo.findOne(id);
    w.decrementBy(4);
    this.repo.save(w);
  }
}

But I don't know how to specify that everything in the updateWidgetStock method should be done with a pessimistic lock set.

There is a Spring Data JPA annotation org.springframework.data.jpa.repository.Lock which allows you to set a LockModeType, but I don't know if it's valid to put it on the updateWidgetStock method. It sounds more like an annotation on the WidgetRepository, because the Javadoc says:

org.springframework.data.jpa.repository
@Target(value=METHOD)
@Retention(value=RUNTIME)
@Documented
public @interface Lock
Annotation used to specify the LockModeType to be used when executing the query. It will be evaluated when using Query on a query method or if you derive the query from the method name.

... so that doesn't seem to be helpful.

How can I make my updateWidgetStock() method execute with LockModeType.PESSIMISTIC_WRITE set?

Answer 1

@Lock is supported on CRUD methods as of version 1.6 of Spring Data JPA (in fact, there's already a milestone available). See this ticket for more details.

With that version you simply declare the following:

interface WidgetRepository extends Repository<Widget, Long> {

  @Lock(LockModeType.PESSIMISTIC_WRITE)
  Widget findOne(Long id);
}

This will cause the CRUD implementation part of the backing repository proxy to apply the configured LockModeType to the find(…) call on the EntityManager.