LockMode in EJB3 Persistence NamedQuery

问题

How do we specify LockMode in EJB3 Persistence NamedQuery? I want to add Pessimistic LockMode to my existing select so that I can update if necessary but surprisingly Query object doesnot have setLockMode(xxx) method ( My understanding was if JPA, asubset of EJB3 persistence, exposes setLockMode, EJB3 persistence should have the method available too).

Query query = em.createNamedQuery("findOptoutStudent");
query.setParameter("optoutIndicator", optoutIndicator);
List<Student> students = query.getResultList();
return students.get(0);

I would assume I dont have to change the query manually to "select for update".

Thanks Kevin

回答1:

Pessimistic Lock Mode :

• PESSIMISTIC_READ which represents a shared lock. Lock request fails when another entity manager has acquired PESSIMISTIC_WRITE.

• PESSIMISTIC_WRITE which represents an exclusive lock. Lock request fails when another entity manager has acquired either of the locks on the object.

Applying lock on the object

entityManager.lock(object, LockModeType.PESSIMISTIC_READ)

Releasing the lock afterwards

entityManager.lock(object, LockModeType.NONE)

来源：https://stackoverflow.com/questions/7839069/lockmode-in-ejb3-persistence-namedquery