Hibernate could not initialize proxy - no Session

问题

My code retrieves all information related to the user:

SessionFactory sessionFactory = HibernateUtilities.configureSessionFactory();
Session session = sessionFactory.openSession();
UserDetails ud = null;
Set<Address> userAddress = null;

try {
    session.beginTransaction();
    ud = (UserDetails) session.get(UserDetails.class, 1);
    userAddress = ud.getAddresses();
    session.getTransaction().commit();
} catch (HibernateException e) {
    e.printStackTrace();
    session.getTransaction().rollback();
} finally {
    session.close();
}

System.out.println(ud.getName());

for(Address addr: userAddress){
    System.out.println("State " + addr.getState());
}

The ud.getAddresses() simply returns a set of Addresses of the user.

My question is: why does the ud object still have its value (eg, name) even though the session is already closed? getAddresses() is an instance variable of the UserDetails class. But why can't I retrieve its value but I can retrieve regular instance variables of the UserDetails class?

ud.getAddresses() is an @EmbeddedCollection.

回答1:

userAddress = ud.getAddresses();
session.getTransaction().commit();
for(Address addr: userAddress) {

The hibernate documentation for working with lazy associations clearly calls out this kind of access as an error. You can interact with lazily associated objects only while the session is still open. That portion of the documentation also provides alternatives to access such lazily associated members of an object and we prefer to specify the fetch mode as JOIN in the criteria used, in our applications.

回答2:

I faced the same issue in JPA/Hibernate, and there are 2 ways to solve this issue:

1/ Turn off the LAZY by default, as following:

@Entity
@Proxy(lazy = false)
public class Project {
...
}

Of course, this way is not recommended because of the performance issue, so you can go to the second way.

2/ You can put @Transactional at the beginning of your method, it can help you to remain the session, or another understanding, it pass the duty of session to Hibernate, as following:

@Test
@Transactional
public void testSaveGroup() {
    Department g = new Department();
    g.setName("XDG");
    assertNull(g.getId());
    this.groupRepo.save(g);
    assertNotNull(g.getId());
    System.out.println(g.getId());
    Project dummyPrj = new Project(123L, "KSTA", new Date(), "NEW", "Helm AG", g);
    this.projectRepo.save(dummyPrj);
    // verify
    List<Department> lst = this.groupRepo.findAll();
    Project savedPrj = this.projectRepo.getOne(123L);
    Assert.assertEquals("XDG", savedPrj.getGroup().getName());
}

My answer is late, but hope to help someone else :)

回答3:

All the primitive properties of the classes are loaded right away, they can't be lazy unless you're using bytecode enhancements. Only real associations like your collection can be lazy.

来源：https://stackoverflow.com/questions/13492410/hibernate-could-not-initialize-proxy-no-session

标签

java

hibernate

persistence

lazy-evaluation

lazy-initialization