hashCode NullPointerException on merge

pfrank13 · **Joined:** Fri Jul 25, 2008 2:53 am **Posts:** 2

Hibernate version: 3.3.2.GA

Code between sessionFactory.openSession() and session.close():
dao.merge(sub);

Full stack trace of any exception that occurs:
java.lang.NullPointerException
at com.example.adplatform.model.Campaign.hashCode(Campaign.java:141)
at java.util.HashMap.put(HashMap.java:372)
at java.util.HashSet.add(HashSet.java:200)
at java.util.AbstractCollection.addAll(AbstractCollection.java:305)
at org.hibernate.collection.PersistentSet.endRead(PersistentSet.java:329)
at org.hibernate.engine.loading.CollectionLoadContext.endLoadingCollection(CollectionLoadContext.java:240)
at org.hibernate.engine.loading.CollectionLoadContext.endLoadingCollections(CollectionLoadContext.java:222)
at org.hibernate.engine.loading.CollectionLoadContext.endLoadingCollections(CollectionLoadContext.java:195)
at org.hibernate.loader.Loader.endCollectionLoad(Loader.java:877)
at org.hibernate.loader.Loader.initializeEntitiesAndCollections(Loader.java:865)
at org.hibernate.loader.Loader.doQuery(Loader.java:729)
at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:236)
at org.hibernate.loader.Loader.loadEntity(Loader.java:1860)
at org.hibernate.loader.entity.AbstractEntityLoader.load(AbstractEntityLoader.java:48)
at org.hibernate.loader.entity.AbstractEntityLoader.load(AbstractEntityLoader.java:42)
at org.hibernate.persister.entity.AbstractEntityPersister.load(AbstractEntityPersister.java:3049)
at org.hibernate.event.def.DefaultLoadEventListener.loadFromDatasource(DefaultLoadEventListener.java:399)
at org.hibernate.event.def.DefaultLoadEventListener.doLoad(DefaultLoadEventListener.java:375)
at org.hibernate.event.def.DefaultLoadEventListener.load(DefaultLoadEventListener.java:139)
at org.hibernate.event.def.DefaultLoadEventListener.proxyOrLoad(DefaultLoadEventListener.java:195)
at org.hibernate.event.def.DefaultLoadEventListener.onLoad(DefaultLoadEventListener.java:103)
at org.hibernate.impl.SessionImpl.fireLoad(SessionImpl.java:878)
at org.hibernate.impl.SessionImpl.internalLoad(SessionImpl.java:846)
at org.hibernate.type.EntityType.resolveIdentifier(EntityType.java:557)
at org.hibernate.type.EntityType.resolve(EntityType.java:379)
at org.hibernate.engine.TwoPhaseLoad.initializeEntity(TwoPhaseLoad.java:120)
at org.hibernate.loader.Loader.initializeEntitiesAndCollections(Loader.java:854)
at org.hibernate.loader.Loader.doQuery(Loader.java:729)
at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:236)
at org.hibernate.loader.Loader.loadEntity(Loader.java:1860)
at org.hibernate.loader.entity.AbstractEntityLoader.load(AbstractEntityLoader.java:48)
at org.hibernate.loader.entity.AbstractEntityLoader.load(AbstractEntityLoader.java:42)
at org.hibernate.persister.entity.AbstractEntityPersister.load(AbstractEntityPersister.java:3049)
at org.hibernate.event.def.DefaultLoadEventListener.loadFromDatasource(DefaultLoadEventListener.java:399)
at org.hibernate.event.def.DefaultLoadEventListener.doLoad(DefaultLoadEventListener.java:375)
at org.hibernate.event.def.DefaultLoadEventListener.load(DefaultLoadEventListener.java:139)
at org.hibernate.event.def.DefaultLoadEventListener.proxyOrLoad(DefaultLoadEventListener.java:195)
at org.hibernate.event.def.DefaultLoadEventListener.onLoad(DefaultLoadEventListener.java:103)
at org.hibernate.impl.SessionImpl.fireLoad(SessionImpl.java:878)
at org.hibernate.impl.SessionImpl.get(SessionImpl.java:815)
at org.hibernate.event.def.DefaultMergeEventListener.entityIsDetached(DefaultMergeEventListener.java:229)
at org.hibernate.event.def.DefaultMergeEventListener.onMerge(DefaultMergeEventListener.java:120)
at org.hibernate.event.def.DefaultMergeEventListener.onMerge(DefaultMergeEventListener.java:53)
at org.hibernate.impl.SessionImpl.fireMerge(SessionImpl.java:677)
at org.hibernate.impl.SessionImpl.merge(SessionImpl.java:661)
at org.hibernate.impl.SessionImpl.merge(SessionImpl.java:665)
at org.hibernate.ejb.AbstractEntityManagerImpl.merge(AbstractEntityManagerImpl.java:235)
at com.example.common.dao.jpa.DaoImpl.merge(DaoImpl.java:81)
at com.example.adplatform.service.impl.AdPlatformServiceImpl.updateSub(AdPlatformServiceImpl.java:859)
at com.example.adplatform.service.impl.AdPlatformServiceTest.testUpdateSubDirectLinkAd(AdPlatformServiceTest.java:2771)
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.internal.runners.TestMethodRunner.executeMethodBody(TestMethodRunner.java:99)
at org.junit.internal.runners.TestMethodRunner.runUnprotected(TestMethodRunner.java:81)
at org.junit.internal.runners.BeforeAndAfterRunner.runProtected(BeforeAndAfterRunner.java:34)
at org.junit.internal.runners.TestMethodRunner.runMethod(TestMethodRunner.java:75)
at org.junit.internal.runners.TestMethodRunner.run(TestMethodRunner.java:45)
at org.junit.internal.runners.TestClassMethodsRunner.invokeTestMethod(TestClassMethodsRunner.java:71)
at org.junit.internal.runners.TestClassMethodsRunner.run(TestClassMethodsRunner.java:35)
at org.junit.internal.runners.TestClassRunner$1.runUnprotected(TestClassRunner.java:42)
at org.junit.internal.runners.BeforeAndAfterRunner.runProtected(BeforeAndAfterRunner.java:34)
at org.junit.internal.runners.TestClassRunner.run(TestClassRunner.java:52)
at org.apache.maven.surefire.junit4.JUnit4TestSet.execute(JUnit4TestSet.java:62)
at org.apache.maven.surefire.suite.AbstractDirectoryTestSuite.executeTestSet(AbstractDirectoryTestSuite.java:140)
at org.apache.maven.surefire.suite.AbstractDirectoryTestSuite.execute(AbstractDirectoryTestSuite.java:127) at org.apache.maven.surefire.Surefire.run(Surefire.java:177)
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.apache.maven.surefire.booter.SurefireBooter.runSuitesInProcess(SurefireBooter.java:338)
at org.apache.maven.surefire.booter.SurefireBooter.main(SurefireBooter.java:997)

Name and version of the database you are using: MySQL 5.0.51b

I'm seeing this NullPointerException when merging an object. I know this bug is related to hibernate.max_fetch_depth setting. If I change it I can eliminate the problem but it becomes unreasonably large. My overriden version of hashcode basically takes a unqiue key and hashcodes the values that make up that key. In this case:

Code:

public class Campaign{
    private TrafficSourceAccount trafficSourceAccount;
    private String name;
.
.
.
    public int hashCode() {
        int result = 17;
        
        Long trafficSourceAccountId;
        if(getTrafficSourceAccount() != null){
            trafficSourceAccountId = getTrafficSourceAccount().getId() == null ? new Long(0L) : getTrafficSourceAccount().getId();
        }else{
            trafficSourceAccountId = new Long(0L);
        }
        
        result = 37 * result + trafficSourceAccountId.hashCode();
        result = 37 * result + getName().hashCode(); //This is the line the NullPointer is thrown
        
        return result;
    }
}

The problem I'm having is this NullPointer is being thrown on an operation of some sort internal to Hibernate. If I execute hashCode() before the merge in my test case the NullPointerException is still thrown during the merge and not when I call it before the merge. I'm assuming that means the Campaign that is in the object I'm merging isn't the issue. It's some other Campaign that is in a collection that is being hydrated as part of this object graph. Does anyone know what the problem is? Is there a better way to override hashCode to avoid this sort of problem in large object graphs?

pfrank13 · **Joined:** Fri Jul 25, 2008 2:53 am **Posts:** 2

OK so I made this much more complicated than it needs to be. I'm seeing the same problem in a much simpler relationship. Let's say just Parent and Child.

Code:

public Parent{
  @Id @GeneratedValue
  private Long id;
  private String name;

  @OneToMany(cascade = CascadeType.ALL, mappedBy="parent")
  private Set<Child> children;
.
.
.
  public Child addChild(Child child){
    child.setParent(this);
    getChildren().add(child);

    return child;
  }
}
---
public Child{
  @Id @GeneratedValue
  private Long id;
  private String name;

  @ManyToOne(fetch = FetchType.EAGER)
  @JoinColumn("parent_id")
  private Parent parent;

  public in hashCode(){
    return getName().hashCode(); //On merge this throws a NullPointer
  }
}
---
---
public void test(){
  beginTransaction();

  Parent parent = new Parent();
  parent.setName("Something");

  Child child = new Child();
  child.setName("SomeChildName");

  parent.addChild(child)

  parentDao.persist(parent);

  closeTransaction();
  beginTransaction();
  
  Child mergedChild = childDao.merge(child);

  closeTransaction();
}

So at the childDao.merge() I can see the child not found in the Session, I can see it retreived, I can then see the Parent being retreived and in it's collection it finds the child that was already retreived but when it is being added to the Set the NPE is thrown. So anyone know what I'm doing wrong in this simplified version of my problem?

woezelmann · **Joined:** Fri Aug 22, 2008 6:12 am **Posts:** 13

I know this is old, but I have the same problem...

Any ideas what this is about?

woezelmann · **Joined:** Fri Aug 22, 2008 6:12 am **Posts:** 13

ok, this seems to be a know issue for more than a year:
http://opensource.atlassian.com/projects/hibernate/browse/HHH-3441?page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel

sanne.grinovero · **Posted:** Wed Feb 03, 2010 6:33 pm

no that's just wrong, you have to write the hashcode in a safer way without assuming all fields to have a value.
The reported issue is using a wrong implementation:

Code:

this.event.getId().hashCode() ^ this.id.hashCode();

is just dangerous, because it assumes the id!=null

same story in this thread:

Quote:

result = 37 * result + getName().hashCode(); //This is the line the NullPointer is thrown

getName() could be null, this is just wrong code in the user class.

Any IDE is able to assist in writing a proper hashCode() implementation

daviderie · **Joined:** Tue May 04, 2010 8:53 am **Posts:** 2

if getName() can be null at one point and non null at a later point, then it can't be used in hashCode() because the hash would change. That is the same reason that database identifiers can't be used in hashCode(). However, getName() shouldn't ever return null if we don't allow it to be set to null, right? Why is Hibernate calling hashCode() on an object before its state is loaded from the database? I am having this issue, and I believe getName() should be usable in hashCode() without checking for null if we don't allow the users of the class to set name to null. So what is going on when Hibernate calls hashCode() before the object's state is loaded?

sanne.grinovero · **Posted:** Wed May 19, 2010 12:58 pm

hibernate didn't call hashCode: you have added it to a Set, likely a HashSet, which will call the hashCode to position the entry internally.
this is plain java.util.collections usage