Hibernate: failed to lazily initialize a collection of role, no session or session was closed

Question

My code:

    @Test public void testAddRoleAndAddUser() {      Role r = roleDao.findByProperty("name", "admin");     if(r == null) {         r = new Role();         r.setName("admin");         r.setDescription("Just administrator.");         roleDao.save(r);     }      User u = dao.get(1l);     Set<Role> roles = u.getRoleSet();     logger.debug("Roles is null: " + (roles == null));     roles.add(r);     dao.save(u); } 

13:39:41,041 ERROR: org.hibernate.LazyInitializationException failed to lazily initialize a collection of role: xxx.entity.core.User.roleSet, no session or session was closed org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: xxx.entity.core.User.roleSet, no session or session was closed at org.hibernate.collection.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:380) at org.hibernate.collection.AbstractPersistentCollection.throwLazyInitializationExceptionIfNotConnected(AbstractPersistentCollection.java:372) at org.hibernate.collection.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:365) at org.hibernate.collection.PersistentSet.add(PersistentSet.java:212) at sg.com.junglemedia.test.dao.impl.hibernate.UserDaoTest.testAddRoleAndAddUser(UserDaoTest.java:40) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:44) at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15) at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:41) at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20) at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:28) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:76) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50) at org.junit.runners.ParentRunner$3.run(ParentRunner.java:193) at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:52) at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:191) at org.junit.runners.ParentRunner.access$000(ParentRunner.java:42) at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:184) at org.junit.runners.ParentRunner.run(ParentRunner.java:236) at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:46) at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)

Anyone help?

Answer 1

In your entity class, when you declare mapping from user to roles, try specifying the fetchType to EAGER. Some thing like this:

@OneToMany(fetch=FetchType.EAGER) public Collection<Role> getRoleSet(){  ... } 

UPDATE: Recent comments this answer's received make me revisit this. It's been a while since I answered, when I only started working with Hibernate. What Rafael and Mukus say are reasonable. If you have a large collection, you shouldn't use eager fetching. It jointly selects all data mapped to your entry and loads to memory. An alternative to this is to still use lazy fetching and open a Hibernate session each time you need to work on the related collection, i.e, each time you need to invoke getRoleSet method. This way, Hibernate will execute the select query to database each time this method is invoked and doesn't keep the collection data in memory. You can refer to my post here for details: http://khuevu.github.io/2013/01/20/understand-hibernate.html

That's said, it can depend on your actual use case. If your collection data is small and you frequently need to query the data, you will better off using eager fetching. I think, in your specific case, a collection of role is probably quite small and suitable to use eager fetching.