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()         


        

Answer 1

If you don't want to override standard findOne() method, you can acquire a lock in your custom method by using select ... for update query just like this:

/**
 * Repository for Wallet.
 */
public interface WalletRepository extends CrudRepository, JpaSpecificationExecutor {

    @Lock(LockModeType.PESSIMISTIC_WRITE)
    @Query("select w from Wallet w where w.id = :id")
    Wallet findOneForUpdate(@Param("id") Long id);
}

However, if you are using PostgreSQL, things can get a little complicated when you want to set lock timeout to avoid deadlocks. PostgreSQL ignores standard property javax.persistence.lock.timeout set in JPA properties or in @QueryHint annotation.

The only way I could get it working was to create a custom repository and set timeout manually before locking an entity. It's not nice but at least it's working:

public class WalletRepositoryImpl implements WalletRepositoryCustom {

@PersistenceContext
private EntityManager em;


@Override
public Wallet findOneForUpdate(Long id) {
    // explicitly set lock timeout (necessary in PostgreSQL)
    em.createNativeQuery("set local lock_timeout to '2s';").executeUpdate();

    Wallet wallet = em.find(Wallet.class, id);

    if (wallet != null) {
        em.lock(wallet, LockModeType.PESSIMISTIC_WRITE);
    }

    return wallet;
}

}