How to refresh cache after persist?

问题:

I am using JPA (EclipseLink 2.5) for persistence. My web app contains AJAX page updates. When a post is saved, the posted content shows up without refreshing the browser. The post have tags associated with it using a OneToMany relationship. These tags are supposed to show up after save too. However, because the cache was enabled I was not able to get the tags.

Here's my code:

   @TransactionAttribute(TransactionAttributeType.REQUIRED)
public Sqask save(AskTag tags) {
    try {
        Sqask ask = saveAsk(tags);
        return ask;
    } catch (Exception e) {
        context.setRollbackOnly();
        return null;
    }
}

public Sqask saveAsk(AskTag tags) {
        Sqask ask = new Sqask();
        ask.setCreator(tags.getAskedBy());
        em.persist(ask);
        em.flush();
        saveTags(tags, ask);
        return ask;
    }

public void saveTags(AskTag tags, Sqask ask) {
        if (!tags.getNask().isEmpty()) {
            NAsk nask = new NAsk();
            NAskPK naskPK = new NAskPK();
            naskPK.setAsk(ask.getId());
            naskPK.setNoun(tags.getNask());
            naskPK.setCreator(tags.getAskedBy().getGuid());
            nask.setNAskPK(naskPK);
            nask.setAsk(ask);
            nask.setCreator(tags.getAskedBy());
            em.persist(nask);
        }

        if (!tags.getVask().isEmpty()) {
            VAsk vask = new VAsk();
            VAskPK vaskPK = new VAskPK();
            vaskPK.setAsk(ask.getId());
            vaskPK.setVerb(tags.getVask());
            vaskPK.setCreator(tags.getAskedBy().getGuid());
            vask.setVAskPK(vaskPK);
            vask.setAsk(ask);
            vask.setCreator(tags.getAskedBy());
            em.persist(vask);
        }

        if (!tags.getForask().isEmpty()) {
            PAsk forask = new PAsk();
            PAskPK foraskPK = new PAskPK();
            foraskPK.setAsk(ask.getId());
            foraskPK.setPrep(tags.getForask());
            foraskPK.setCreator(tags.getAskedBy().getGuid());
            forask.setPAskPK(foraskPK);
            forask.setAsk(ask);
            forask.setCreator(tags.getAskedBy());
            em.persist(forask);
        }

        if (!tags.getAboutask().isEmpty()) {
            PAsk aboutask = new PAsk();
            PAskPK aboutaskPK = new PAskPK();
            aboutaskPK.setAsk(ask.getId());
            aboutaskPK.setPrep(tags.getAboutask());
            aboutaskPK.setCreator(tags.getAskedBy().getGuid());
            aboutask.setPAskPK(aboutaskPK);
            aboutask.setAsk(ask);
            aboutask.setCreator(tags.getAskedBy());
            em.persist(aboutask);
        }

        em.getEntityManagerFactory().getCache().evict(Sqask.class, ask.getId());
        em.merge(ask);
}

How can I get things to work? How to refresh an entity with all its associated entities? Thanks.

回答1:

If I understand your question correctly maybe this could help you - please notice em.refresh call before returning. This ensured that all OneToOne and OneToMany joins are refreshed, even if you are only saving an ID of related record.

public T create(T entity) {
  em.persist(entity);
  em.flush();
  em.refresh(entity); // this could be important
  return entity;
}

回答2:

I am not pretty sure whether it will work or not but please try this in your code if its the problem of backend.

em.merge(ask);
 ask.getId();

or

 em.merge(ask);
 ask.getId();
 ask.getCollection1ofAsk().size();
 ask.getCollection2OfAsk().size();
.....

回答3:

After added em.flush() before em.refresh(ask), the code worked as I intended. It fetched the lists related to the entity ask. Could anyone explain why? Thanks very much

回答4:

It could be an AJAX cache problem as well. The reason is if your using javascript for AJAX, you could end up with caching issues. Just check it.. If you think the problem is with JPA cache, working around entity manager with flush and refresh will solve the issue