EntityManager refresh | 易学教程

问题

I have web application using JPA. This entity manager keeps bunch of entites and suddenly I update the database from other side. I use MySQL and I use PhpMyAdmin and change some row.

How to tell entity manager to re-synchronize, e.g. to forgot all the entites in cache?

I know there is refresh(Object) method, but is there any possibility how to do refreshAll() or something what results in this?

It is sure this is expensive operation but if it has to be done.

回答1:

entityManager.getEntityManagerFactory().getCache().evictAll()

Refresh is something different since it modifies your object. This line will just empty the cache, so if you fetch objects changed outside the entity manager, it will do an actual database query instead of using the outdated cached value.

回答2:

I had a similar issue and the evictAll() line above worked for me.

Alternatively, the @Cache annotation on the entity class worked too, with the benefit of being able to control caching parameters:

@Cache(coordinationType=CacheCoordinationType.INVALIDATE_CHANGED_OBJECTS)

See: http://wiki.eclipse.org/EclipseLink/Examples/JPA/Caching

回答3:

Well, for some people (like me) that tried to add factory.getCache().evictAll(); and doesn't work, and are used JPA + Hibernate, to refresh a query add the hint org.hibernate.cacheMode to IGNORE. Example:

em.createNamedQuery("SomeEntity.SomeNamedQuery")
  .setHint("org.hibernate.cacheMode", "IGNORE")
  .getResultList();

回答4:

cache.evictAll is not working for me. So to retrieve data pushed from another app, I peform :

em.getTransaction().begin();
em.getTransaction().commit();

After that, my find query retrieves refreshed data. I don't know if it's very safe solution but it works properly.

回答5:

If you are using EclipseLink instead of Hibernate the hint is:

em.createNamedQuery("SomeEntity.SomeNamedQuery")
.setHint(QueryHints.REFRESH, true)
.getResultList();

回答6:

When you read an object into an EntityManager, it becomes part of the persistence context, and the same object will remain in the EntityManager until you either clear() it and get a new EntityManager. So if you update the database, the EntityManager will not see the change unless you call refresh() on the object, or clear() the EntityManager. This has nothing to do with the shared cache (L2) or the persistence context (L1). If you also also using a shared cache, and updating the database directly, then your shared cache will be out of date. You need to refresh() the object, or mark it as invalid to be refreshed the next time it is queried.

Code must follow the way like. DETACH REFRESH MERGE FLUSH

来源：https://stackoverflow.com/questions/5832415/entitymanager-refresh

标签

java

jpa

entitymanager