Examples of org.hibernate.collection.spi.PersistentCollection

org.hibernate.collection.spi.PersistentCollection
Persistent collections are treated as value objects by Hibernate. ie. they have no independent existence beyond the object holding a reference to them. Unlike instances of entity classes, they are automatically deleted when unreferenced and automatically become persistent when held by a persistent object. Collections can be passed between different objects (change "roles") and this might cause their elements to move from one database table to another.

Hibernate "wraps" a java collection in an instance of PersistentCollection. This mechanism is designed to support tracking of changes to the collection's persistent state and lazy instantiation of collection elements. The downside is that only certain abstract collection types are supported and any extra semantics are lost

Applications should never use classes in this package directly, unless extending the "framework" here.

Changes to structure of the collection are recorded by the collection calling back to the session. Changes to mutable elements (ie. composite elements) are discovered by cloning their state when the collection is initialized and comparing at flush time. @author Gavin King

   * @param key The key of the collection's entry.
   */
  private void addCollection(PersistentCollection coll, CollectionEntry entry, Serializable key) {
    collectionEntries.put( coll, entry );
    CollectionKey collectionKey = new CollectionKey( entry.getLoadedPersister(), key );
    PersistentCollection old = ( PersistentCollection ) collectionsByKey.put( collectionKey, coll );
    if ( old != null ) {
      if ( old == coll ) {
        throw new AssertionFailure("bug adding collection twice");
      }
      // or should it actually throw an exception?
      old.unsetSession( session );
      collectionEntries.remove( old );
      // watch out for a case where old is still referenced
      // somewhere in the object graph! (which is a user error)
    }
  }

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   * Get the collection entry for a collection passed to filter,
   * which might be a collection wrapper, an array, or an unwrapped
   * collection. Return null if there is no entry.
   */
  public CollectionEntry getCollectionEntryOrNull(Object collection) {
    PersistentCollection coll;
    if ( collection instanceof PersistentCollection ) {
      coll = (PersistentCollection) collection;
      //if (collection==null) throw new TransientObjectException("Collection was not yet persistent");
    }
    else {
      coll = getCollectionHolder(collection);
      if ( coll == null ) {
        //it might be an unwrapped collection reference!
        //try to find a wrapper (slowish)
        Iterator wrappers = IdentityMap.keyIterator(collectionEntries);
        while ( wrappers.hasNext() ) {
          PersistentCollection pc = (PersistentCollection) wrappers.next();
          if ( pc.isWrapper(collection) ) {
            coll = pc;
            break;
          }
        }
      }

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      count = ois.readInt();
      if ( tracing ) LOG.trace("Starting deserialization of [" + count + "] collectionEntries entries");
      rtn.collectionEntries = IdentityMap.instantiateSequenced( count < INIT_COLL_SIZE ? INIT_COLL_SIZE : count );
      for ( int i = 0; i < count; i++ ) {
        final PersistentCollection pc = ( PersistentCollection ) ois.readObject();
        final CollectionEntry ce = CollectionEntry.deserialize( ois, session );
        pc.setCurrentSession( session );
        rtn.collectionEntries.put( pc, ce );
      }


      count = ois.readInt();
      if ( tracing ) LOG.trace("Starting deserialization of [" + count + "] arrayHolders entries");

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          //    with the current Session
          //throw new AssertionFailure("bug loading unowned collection");
        }
      }


      PersistentCollection rowCollection = persistenceContext.getLoadContexts()
          .getCollectionLoadContext( rs )
          .getLoadingCollection( persister, collectionRowKey );


      if ( rowCollection != null ) {
        rowCollection.readFrom( rs, persister, descriptor, owner );
      }


    }
    else if ( optionalKey != null ) {
      // we did not find a collection element in the result set, so we

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   * @param key The key of the collection's entry.
   */
  private void addCollection(PersistentCollection coll, CollectionEntry entry, Serializable key) {
    collectionEntries.put( coll, entry );
    CollectionKey collectionKey = new CollectionKey( entry.getLoadedPersister(), key );
    PersistentCollection old = collectionsByKey.put( collectionKey, coll );
    if ( old != null ) {
      if ( old == coll ) {
        throw new AssertionFailure("bug adding collection twice");
      }
      // or should it actually throw an exception?
      old.unsetSession( session );
      collectionEntries.remove( old );
      // watch out for a case where old is still referenced
      // somewhere in the object graph! (which is a user error)
    }
  }

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   * which might be a collection wrapper, an array, or an unwrapped
   * collection. Return null if there is no entry.
   */
  @Override
  public CollectionEntry getCollectionEntryOrNull(Object collection) {
    PersistentCollection coll;
    if ( collection instanceof PersistentCollection ) {
      coll = (PersistentCollection) collection;
      //if (collection==null) throw new TransientObjectException("Collection was not yet persistent");
    }
    else {
      coll = getCollectionHolder(collection);
      if ( coll == null ) {
        //it might be an unwrapped collection reference!
        //try to find a wrapper (slowish)
        Iterator<PersistentCollection> wrappers = collectionEntries.keyIterator();
        while ( wrappers.hasNext() ) {
          PersistentCollection pc = wrappers.next();
          if ( pc.isWrapper(collection) ) {
            coll = pc;
            break;
          }
        }
      }

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      count = ois.readInt();
      if ( tracing ) LOG.trace("Starting deserialization of [" + count + "] collectionEntries entries");
      rtn.collectionEntries = IdentityMap.instantiateSequenced( count < INIT_COLL_SIZE ? INIT_COLL_SIZE : count );
      for ( int i = 0; i < count; i++ ) {
        final PersistentCollection pc = ( PersistentCollection ) ois.readObject();
        final CollectionEntry ce = CollectionEntry.deserialize( ois, session );
        pc.setCurrentSession( session );
        rtn.collectionEntries.put( pc, ce );
      }


      count = ois.readInt();
      if ( tracing ) LOG.trace("Starting deserialization of [" + count + "] arrayHolders entries");

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    final LinkedHashMap<CollectionEntry, PersistentCollection> map =  batchLoadableCollections.get( collectionPersister.getRole() );
    if ( map != null ) {
      for ( Map.Entry<CollectionEntry, PersistentCollection> me : map.entrySet() ) {
        final CollectionEntry ce = me.getKey();
        final PersistentCollection collection = me.getValue();
        
        if ( ce.getLoadedKey() == null ) {
          // the loadedKey of the collectionEntry might be null as it might have been reset to null
          // (see for example Collections.processDereferencedCollection()
          // and CollectionEntry.afterAction())
          // though we clear the queue on flush, it seems like a good idea to guard
          // against potentially null loadedKeys (which leads to various NPEs as demonstrated in HHH-7821).
          continue;
        }


        if ( collection.wasInitialized() ) {
          // should never happen
          LOG.warn( "Encountered initialized collection in BatchFetchQueue, this should not happen." );
          continue;
        }

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          //    with the current Session
          //throw new AssertionFailure("bug loading unowned collection");
        }
      }


      PersistentCollection rowCollection = persistenceContext.getLoadContexts()
          .getCollectionLoadContext( rs )
          .getLoadingCollection( persister, collectionRowKey );


      if ( rowCollection != null ) {
        rowCollection.readFrom( rs, persister, descriptor, owner );
      }


    }
    else if ( optionalKey != null ) {
      // we did not find a collection element in the result set, so we

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    if ( collection == null ) {
      //do nothing
    }
    else if ( collection instanceof PersistentCollection ) {
      PersistentCollection persistentCollection = ( PersistentCollection ) collection;
      if ( persistentCollection.setCurrentSession( session ) ) {
        if ( isOwnerUnchanged( persistentCollection, persister, extractCollectionKeyFromOwner( persister ) ) ) {
          // a "detached" collection that originally belonged to the same entity
          if ( persistentCollection.isDirty() ) {
            throw new HibernateException( "reassociated object has dirty collection" );
          }
          reattachCollection( persistentCollection, type );
        }
        else {

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org.hibernate.action.internal.CollectionRemoveAction

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org.hibernate.action.internal.QueuedOperationCollectionAction

org.hibernate.engine.internal.StatefulPersistenceContext

org.hibernate.engine.loading.internal.CollectionLoadContext

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