EntityManager doesn't refresh the data after querying

问题

My current project uses HSQLDB2.0 and JPA2.0 .

The scenario is: I query DB to get list of contactDetails of person. I delete single contactInfo at UI but do not save that data (Cancel the saving part).

I again do the same query, now the result list is 1 lesser than previous result coz I have deleted one contactInfo at UI. But that contactInfo is still available at DB if I cross check.

But if I include entityManager.clear() before start of the query, I get correct results every time.

I dont understand this behaviour. Could anyone make it clear for me?

回答1:

Rather than querying again, try this:

entityManager.refresh(person);

A more complete example:

EntityManagerFactory factory = Persistence.createEntityManagerFactory("...");
EntityManager em = factory.createEntityManager();
em.getTransaction().begin();

Person p = (Person) em.find(Person.class, 1);
assertEquals(10, p.getContactDetails().size()); // let's pretend p has 10 contact details
p.getContactDetails().remove(0);
assertEquals(9, p.getContactDetails().size());

Person p2 = (Person) em.find(Person.class, 1);
assertTrue(p == p2); // We're in the same persistence context so p == p2
assertEquals(9, p.getContactDetails().size());

// In order to reload the actual patients from the database, refresh the entity
em.refresh(p);
assertTrue(p == p2);
assertEquals(10, p.getContactDetails().size());
assertEquals(10, p2.getContactDetails().size());

em.getTransaction().commit();
em.close();
factory.close();

回答2:

The behaviour of clear() is explained in its javadoc:

Clear the persistence context, causing all managed entities to become detached. Changes made to entities that have not been flushed to the database will not be persisted.

That is, removal of contactInfo is not persisted.

ContactInfo is not getting removed from the database because you remove the relationship between ContactDetails and ContactInfo, but not ContactInfo itself. If you want to remove it, you need either do it explicitly with remove() or specify orphanRemoval = true on the relationship.

来源：https://stackoverflow.com/questions/5295386/entitymanager-doesnt-refresh-the-data-after-querying