many-to-one property-ref causing null exception

ustinov · **Joined:** Wed Jul 26, 2006 6:01 am **Posts:** 10

We have the same problem...

Code:

   private void addGroup2Group(){
      Integer parentgroupid = null;
      Integer childgroupid = null;
      BufferedReader d = new BufferedReader(new InputStreamReader(System.in));
      
      System.out.println("Wählen Sie eine Gruppe aus(Parent):");
      listGroups();
      
      try {
         parentgroupid = Integer.valueOf(d.readLine());
         System.out.println("Wählen Sie eine Gruppe aus(Child):");
         listGroups();
         childgroupid = Integer.valueOf(d.readLine());
      } catch (NumberFormatException e) {
         System.out.println("Nummer Eingeben!!!!");
         return;
      } catch (IOException e) {
         e.printStackTrace();
         return;
      }
      
      session = HibernateUtil.getSessionFactory().openSession();
      session.beginTransaction();
      
      PGroup child = (PGroup) session.load(PGroup.class, childgroupid);
      PGroup parent = (PGroup) session.load(PGroup.class, parentgroupid);
      
// With this line, the function works well !!!!
//      child.getName();
      
      if (parent == null){
         System.out.println("Es existiert keine Gruppe mit dieser ID:" + parentgroupid);
         return;
      }
      if (child == null){
         System.out.println("Es existiert keine Gruppe mit dieser ID:" + childgroupid);
         return;
      }
      
      parent.getElements().add(child);
      session.flush();
      session.getTransaction().commit();
      
      System.out.println("Gruppe : " + child.getName() + " wurde erfolgreich zu der Gruppe : " + parent.getName() + " hinzugefügt!");
      
      session.close();
   }

Error message:

Code:

27.07.2006 14:41:59 org.hibernate.AssertionFailure <init>
SCHWERWIEGEND: an assertion failure occured (this may indicate a bug in Hibernate, but is more likely due to unsafe use of the session)
org.hibernate.AssertionFailure: collection [database.structure.PGroup.Elements] was not processed by flush()
   at org.hibernate.engine.CollectionEntry.postFlush(CollectionEntry.java:205)
   at org.hibernate.event.def.AbstractFlushingEventListener.postFlush(AbstractFlushingEventListener.java:332)
   at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:28)
   at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:993)
   at org.hibernate.impl.SessionImpl.managedFlush(SessionImpl.java:340)
   at org.hibernate.transaction.JDBCTransaction.commit(JDBCTransaction.java:106)
   at logic.Hello.addGroup2Group(Hello.java:303)
   at logic.Hello.groupManager(Hello.java:241)
   at logic.Hello.groupManager(Hello.java:254)
   at logic.Hello.menu(Hello.java:31)
   at logic.Hello.main(Hello.java:385)

Has anybody an idea?

tenwit · **Joined:** Thu Dec 23, 2004 9:08 pm **Posts:** 2008

Still no idea, though your comment saying that accessing member property makes it work gave me a new lead to track down in the code. No joy though, I can't see any conditionals that might have caused a collection to be skipped during processing: the only escapes from that flow of control seem to be exceptions. And seeing as there's no other exceptions being reported, I'm at a loss.

joj46: As a matter of interest, if you access a member of the User entity before adding it to the Call, does the exception go away?

Code:

user = getUserByID();
user.getName(); // New line to force User entity to be processed.
call = new call();
call.setAgent(user);
makePersistent(call); 

If it does, that would suggest a definite bug. We could search jira for this issue, it's bound to have come up before.

ustinov · **Joined:** Wed Jul 26, 2006 6:01 am **Posts:** 10

HI,

I solved my problem as follows:

In order to add an Element to the "SET" we have to override 2 methods:

see: http://www.hibernate.org/hib_docs/v3/re ... lshashcode

now everything functions

jojo46 · **Joined:** Mon Jun 19, 2006 9:21 pm **Posts:** 25

So I'm not sure which solution it was, but I first tried implementing the hash and the equals methods, but that didn't work. Then, when I added user.getUsername() it did. So I guess maybe you have to do both, make the hash and equals methods as well as actually getting whatever prop-ref your mapping refers to.
And tenwit, this has to be a bug. There is no conceivable reason why I should have to actually do a get on the property I'm refering to...at least I can't see a reason.

For those interested here's the little snippet of code that got it working for me

User user = DAOFactory.DEFAULT.getUserDAO().findById(this.getUserId());
user.getUsername();
call = new HomestudyCall();
call.setId(TokenGenerator.getUniqueID());
call.setAgent(user);

Pretty straight forward, but odd that I had to do that.

jojo46 · **Joined:** Mon Jun 19, 2006 9:21 pm **Posts:** 25

One more thing.....if you don't want to use a persistent class, but a transient one you can. Make sure you set the id of the transient class you are using. IE:
User user = new User();
user.setId(this.getUserId());
user.setUsername(this.getUserName());
user.getUsername();
call = new HomestudyCall();
call.setId(TokenGenerator.getUniqueID());
call.setAgent(user);

Tried it and it works....this was my original issue that ballooned into the new one.

I have a new question though (and I should probably start a new thread, but it's a fairly simple question...I think ). Whenever I insert a call using the above it does a select for the user when inserting the call. Is there a way to not have it do so...I know the user exists through other means, so I don't need hibernate to check that. I've noticed quite a few of my many-to-one do a select before inserting, but others, that have the same configuration, don't. Wasn't sure why that was happening, but I'd like to get it to stop that if I could. It's just more hits on the database that will end up causing me headaches later down the line when concurrent usage of the system gets larger.

tenwit · **Joined:** Thu Dec 23, 2004 9:08 pm **Posts:** 2008

In that code snippet you don't need the user.getUsername(). If that's needed, it's only because it forces hibernate to load the entity; you're creating a transient entity, getUsername() isn't going to affect that.

Your question doesn't look too simple to me. You have unidirectional many-to-one associations in various places, and some mappings force a load of the one-end when inserting a new element on the many-end? But some mappings don't? Sounds very weird. You say you've just implemented hashCode() and equals(): perhaps you've done that wrong? There are a lot of rules about how to implement those methods, and if you do it wrong, there are a multitude of potential errors waiting for you.

Some rules for hashCode and equals methods in persitent classes:

Don't refer to the DB id
Don't refer to related objects, whether in a colleciton or a simple association
Don't refer to often-changed properties like version numbers or timestamps

sterdomi · **Joined:** Mon Jan 23, 2006 10:06 am **Posts:** 4

This error occurs also in special mapping conditions:
27.07.2006 14:41:59 org.hibernate.AssertionFailure <init>
SCHWERWIEGEND: an assertion failure occured (this may indicate a bug in Hibernate, but is more likely due to unsafe use of the session)
org.hibernate.AssertionFailure: collection [database.structure.PGroup.Elements] was not processed by flush()
at org.hibernate.engine.CollectionEntry.postFlush(CollectionEntry.java:205)
at org.hibernate.event.def.AbstractFlushingEventListener.postFlush(AbstractFlushingEventListener.java:332)
at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:28)
at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:993)
at org.hibernate.impl.SessionImpl.managedFlush(SessionImpl.java:340)
at org.hibernate.transaction.JDBCTransaction.commit(JDBCTransaction.java:106)

mapping one:
User to paramValues:

Code:

<set name="paramValues" table="ParameterValue" inverse="true" cascade="all,delete-orphan" [b]lazy="false"[/b]>
         <key column="USER_FK_ID"/>
<one-to-many class="ParameterValue"/>
</set>

mapping two:
ParameterValue to user:

Code:

<many-to-one name="user" foreign-key="FK_PARAMVALUE_TO_USER">
<column name="USER_FK_ID" length="40"/>
</many-to-one>

if you load the paramvalues and the user over a criteria (which has the paramValues eager fetched) it will occur the error mentioned above.

I'm using ThreadLocal- and session-per-conversation Pattern

Best regards
Dominic