[hibernate-issues] [Hibernate-JIRA] Created: (HHH-3121) Using fetch="subselect" and second level cache causes NullPointerException

[Adam Brod (JIRA)]

Using fetch="subselect" and second level cache causes NullPointerException
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                 Key: HHH-3121
                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-3121
             Project: Hibernate3
          Issue Type: Bug
          Components: caching (L2)
    Affects Versions: 3.2.6
         Environment: Oracle 10g
            Reporter: Adam Brod


I've been tuning some of our mappings to use fetch="subselect" to reduce the number of DB queries.  However, I have run into two cases where I get the exception below.  In both cases, I was loading a list of Videos, which are mapped to a list of other objects.  (In this example, Media is the superclass of Video.)  I apologize that I can't upload a full working example, but I will include the relevant mapping info.

<class name="Media" table="media" lazy="false" discriminator-value="0">
  <cache usage="nonstrict-read-write"/>  	
  <id name="id" column="id" type="long">
	<generator class="seqhilo"><param name="sequence">hibernate_hi_sequence</param><param name="max_lo">500</param></generator>    	
  </id>
  ...
    <list name="tags" lazy="true" table="media_tags" cascade="save-update" fetch="subselect">
	<cache usage="nonstrict-read-write"/>  	    	      
      <key column="media_id"/>
      <list-index column="idx"/>      
      <many-to-many column="tag_id" class="com.brightcove.catalog.Tag"/>
    </list>
   ...
  <subclass name="Video" lazy="false" discriminator-value="1">
   ...
  </subclass>
</class>
<class name="Tag" table="tag">
...
</class>

The HQL being executed is just a simple "from Video v where v.publisher_id = :pubId".

The line of code where the exception is generated in Video.getDTO() is accessing the Tags list:
for (Tag tag : getTags()) {
    tags.add(tag.getDTO());
}

I've debugged into the Hibernate source to see where the NPE comes from (CollectionLoadContext line 298).

if ( persister.isVersioned() ) {
  versionComparator = persister.getOwnerEntityPersister().getVersionType().getComparator();
  final Object collectionOwner = getLoadContext().getPersistenceContext().getCollectionOwner( lce.getKey(), persister );
  version = getLoadContext().getPersistenceContext().getEntry( collectionOwner ).getVersion(); //NPE!
}

It seems that "collectionOwner" is null, so calling getEntry(collectionOwner) returns null.  Calling getVersion() on a null entry is what throws the NPE.


java.lang.NullPointerException
        at org.hibernate.engine.loading.CollectionLoadContext.addCollectionToCache(CollectionLoadContext.java:298)
        at org.hibernate.engine.loading.CollectionLoadContext.endLoadingCollection(CollectionLoadContext.java:256)
        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.loadCollectionSubselect(Loader.java:2066)
        at org.hibernate.loader.collection.SubselectCollectionLoader.initialize(SubselectCollectionLoader.java:58)
        at org.hibernate.persister.collection.AbstractCollectionPersister.initialize(AbstractCollectionPersister.java:565)
        at org.hibernate.event.def.DefaultInitializeCollectionEventListener.onInitializeCollection(DefaultInitializeCollectionEventListener.java:60)
        at org.hibernate.impl.SessionImpl.initializeCollection(SessionImpl.java:1716)
        at org.hibernate.collection.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:344)
        at org.hibernate.collection.AbstractPersistentCollection.read(AbstractPersistentCollection.java:86)
        at org.hibernate.collection.AbstractPersistentCollection.readSize(AbstractPersistentCollection.java:109)
        at org.hibernate.collection.PersistentList.size(PersistentList.java:91)
        at com.brightcove.catalog.EconomicEntity.populateDTO(EconomicEntity.java:460)
        at com.brightcove.catalog.Media.populateDTO(Media.java:192)
        at com.brightcove.catalog.Video.populateDTO(Video.java:854)
        at com.brightcove.catalog.Video.getDTO(Video.java:783)
        at com.brightcove.catalog.Video.getDTO(Video.java:756)

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