Examples of org.hibernate.collection.PersistentCollection

org.hibernate.collection.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


      count = ois.readInt();
      log.trace( "staring 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();
      log.trace( "staring deserialization of [" + count + "] arrayHolders entries" );

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  public void execute() throws HibernateException {
    final Serializable id = getKey();
    final SessionImplementor session = getSession();
    final CollectionPersister persister = getPersister();
    final PersistentCollection collection = getCollection();
    boolean affectedByFilters = persister.isAffectedByEnabledFilters(session);


    preUpdate();


    if ( !collection.wasInitialized() ) {
      if ( !collection.hasQueuedOperations() ) throw new AssertionFailure( "no queued adds" );
      //do nothing - we only need to notify the cache...
    }
    else if ( !affectedByFilters && collection.empty() ) {
      if ( !emptySnapshot ) persister.remove( id, session );
    }
    else if ( collection.needsRecreate(persister) ) {
      if (affectedByFilters) {
        throw new HibernateException(
          "cannot recreate collection while filter is enabled: " + 
          MessageHelper.collectionInfoString( persister, id, persister.getFactory() )
        );

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  }


  public void execute() throws HibernateException {
    // this method is called when a new non-null collection is persisted
    // or when an existing (non-null) collection is moved to a new owner
    final PersistentCollection collection = getCollection();
    
    preRecreate();


    getPersister().recreate( collection, getKey(), getSession() );

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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 (entityMode==EntityMode.DOM4J && !isEmbeddedInXML) {
      return UNFETCHED_COLLECTION;
    }
    
    // check if collection is currently being loaded
    PersistentCollection collection = persistenceContext.getLoadContexts().locateLoadingCollection( persister, key );
    
    if ( collection == null ) {
      
      // check if it is already completely loaded, but unowned
      collection = persistenceContext.useUnownedCollection( new CollectionKey(persister, key, entityMode) );
      
      if ( collection == null ) {
        // create a new collection wrapper, to be initialized later
        collection = instantiate( session, persister, key );
        collection.setOwner(owner);
  
        persistenceContext.addUninitializedCollection( persister, collection, key );
  
        // some collections are not lazy:
        if ( initializeImmediately( entityMode ) ) {
          session.initializeCollection( collection, false );
        }
        else if ( !persister.isLazy() ) {
          persistenceContext.addNonLazyCollection( collection );
        }
  
        if ( hasHolder( entityMode ) ) {
          session.getPersistenceContext().addCollectionHolder( collection );
        }
        
      }
      
    }
    
    collection.setOwner(owner);


    return collection.getValue();
  }

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    Iterator iter = context.getCollectionEntries().entrySet().iterator(); //TODO: calling entrySet on an IdentityMap is SLOW!!
    while ( iter.hasNext() ) {
      Map.Entry me = (Map.Entry) iter.next();


      CollectionEntry ce = (CollectionEntry) me.getValue();
      PersistentCollection collection = (PersistentCollection) me.getKey();
      if ( !collection.wasInitialized() && ce.getLoadedPersister() == collectionPersister ) {


        if ( checkForEnd && i == end ) {
          return keys; //the first key found after the given key
        }

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  throws HibernateException {


    if ( collection!=null && (collection instanceof PersistentCollection) ) {


      final SessionImplementor session = getSession();
      PersistentCollection coll = (PersistentCollection) collection;
      if ( coll.setCurrentSession(session) ) {
        reattachCollection( coll, collectionType );
      }
      return null;


    }

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      //TODO: move into collection type, so we can use polymorphism!
      if ( collectionType.hasHolder( session.getEntityMode() ) ) {
        
        if (collection==CollectionType.UNFETCHED_COLLECTION) return null;


        PersistentCollection ah = persistenceContext.getCollectionHolder(collection);
        if (ah==null) {
          ah = collectionType.wrap(session, collection);
          persistenceContext.addNewCollection( persister, ah );
          persistenceContext.addCollectionHolder(ah);
        }
        return null;
      }
      else {


        PersistentCollection persistentCollection = collectionType.wrap(session, collection);
        persistenceContext.addNewCollection( persister, persistentCollection );


        if ( log.isTraceEnabled() ) log.trace( "Wrapped collection in role: " + collectionType.getRole() );


        return persistentCollection; //Force a substitution!

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   * called by a collection that wants to initialize itself
   */
  public void onInitializeCollection(InitializeCollectionEvent event)
  throws HibernateException {


    PersistentCollection collection = event.getCollection();
    SessionImplementor source = event.getSession();


    CollectionEntry ce = source.getPersistenceContext().getCollectionEntry(collection);
    if (ce==null) throw new HibernateException("collection was evicted");
    if ( !collection.wasInitialized() ) {
      if ( log.isTraceEnabled() ) {
        log.trace(
            "initializing collection " +
            MessageHelper.collectionInfoString( ce.getLoadedPersister(), ce.getLoadedKey(), source.getFactory() )
          );

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    EventSource session = getSession();
    CollectionPersister persister = session.getFactory().getCollectionPersister( type.getRole() );


    final Serializable collectionKey = extractCollectionKeyFromOwner( persister );
    if ( collection!=null && (collection instanceof PersistentCollection) ) {
      PersistentCollection wrapper = (PersistentCollection) collection;
      if ( wrapper.setCurrentSession(session) ) {
        //a "detached" collection!
        if ( !isOwnerUnchanged( wrapper, persister, collectionKey ) ) {
          // if the collection belonged to a different entity,
          // clean up the existing state of the collection
          removeCollection( persister, collectionKey, session );

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