HHH-17953 fix StatelessSession.fetch() for empty collection

Signed-off-by: Gavin King <gavin@hibernate.org>

Author: gavinking

hibernate-core/src/main/java/org/hibernate/event/internal/DefaultInitializeCollectionEventListener.java

@@ -20,7 +20,6 @@
 import org.hibernate.internal.CoreLogging;
 import org.hibernate.internal.CoreMessageLogger;
 import org.hibernate.persister.collection.CollectionPersister;
-import org.hibernate.pretty.MessageHelper;
 import org.hibernate.sql.results.internal.ResultsHelper;
 import org.hibernate.stat.spi.StatisticsImplementor;
 
@@ -39,7 +38,8 @@ public void onInitializeCollection(InitializeCollectionEvent event) throws Hiber
 final PersistentCollection<?> collection = event.getCollection();
 final SessionImplementor source = event.getSession();
 
-final CollectionEntry ce = source.getPersistenceContextInternal().getCollectionEntry( collection );
+final PersistenceContext persistenceContext = source.getPersistenceContextInternal();
+final CollectionEntry ce = persistenceContext.getCollectionEntry( collection );
 if ( ce == null ) {
 throw new HibernateException( "collection was evicted" );
 }
@@ -65,7 +65,7 @@ public void onInitializeCollection(InitializeCollectionEvent event) throws Hiber
 LOG.trace( "Collection not cached" );
 }
 loadedPersister.initialize( loadedKey, source );
-handlePotentiallyEmptyCollection( collection, source, ce, loadedPersister );
+handlePotentiallyEmptyCollection( collection, persistenceContext, loadedKey, loadedPersister );
 if ( LOG.isTraceEnabled() ) {
 LOG.trace( "Collection initialized" );
 }
@@ -78,18 +78,18 @@ public void onInitializeCollection(InitializeCollectionEvent event) throws Hiber
 }
 }
 
-private void handlePotentiallyEmptyCollection(
+public static void handlePotentiallyEmptyCollection(
 PersistentCollection<?> collection,
-SessionImplementor source,
-CollectionEntry ce,
+PersistenceContext persistenceContext,
+Object loadedKey,
 CollectionPersister loadedPersister) {
 if ( !collection.wasInitialized() ) {
 collection.initializeEmptyCollection( loadedPersister );
 ResultsHelper.finalizeCollectionLoading(
-source.getPersistenceContext(),
+persistenceContext,
 loadedPersister,
 collection,
-ce.getLoadedKey(),
+loadedKey,
 true
 );
 }

hibernate-core/src/main/java/org/hibernate/internal/StatelessSessionImpl.java

@@ -49,6 +49,7 @@
 import static org.hibernate.engine.internal.Versioning.incrementVersion;
 import static org.hibernate.engine.internal.Versioning.seedVersion;
 import static org.hibernate.engine.internal.Versioning.setVersion;
+import static org.hibernate.event.internal.DefaultInitializeCollectionEventListener.handlePotentiallyEmptyCollection;
 import static org.hibernate.generator.EventType.INSERT;
 import static org.hibernate.internal.util.NullnessUtil.castNonNull;
 import static org.hibernate.pretty.MessageHelper.infoString;
@@ -503,6 +504,8 @@ else if ( association instanceof PersistentCollection ) {
 persistentCollection.setCurrentSession( this );
 try {
 collectionDescriptor.initialize( key, this );
+handlePotentiallyEmptyCollection( persistentCollection, getPersistenceContextInternal(), key,
+collectionDescriptor );
 }
 finally {
 persistentCollection.unsetSession( this );

hibernate-core/src/test/java/org/hibernate/orm/test/bytecode/enhancement/lazy/fetch/FetchTest.java

@@ -89,6 +89,33 @@ public void testFetch() {
 long count = stats.getPrepareStatementCount();
 session.fetch( school.students);
 assertTrue( Hibernate.isInitialized( school.students) );
+assertEquals( 1, school.students.size() );
+
+assertEquals( count+1, stats.getPrepareStatementCount() );
+}
+);
+}
+
+@Test
+public void testFetchEmpty() {
+inStatelessTransaction(
+session -> {
+Secondary secondary = new Secondary( "BHS" );
+session.insert(secondary);
+}
+);
+
+inStatelessSession(
+session -> {
+final Statistics stats = sessionFactory().getStatistics();
+stats.clear();
+final School school = session.get( School.class, "BHS" );
+assertFalse( Hibernate.isInitialized( school.students) );
+assertTrue( school.students instanceof PersistentSet );
+long count = stats.getPrepareStatementCount();
+session.fetch( school.students);
+assertTrue( Hibernate.isInitialized( school.students) );
+assertTrue( school.students.isEmpty() );
 
 assertEquals( count+1, stats.getPrepareStatementCount() );
 }