HHH-16624 Do not create subselects when there are fewer than 2 results

hibernate-core/src/main/java/org/hibernate/engine/spi/SubselectFetch.java

@@ -13,15 +13,12 @@
 import java.util.Set;
 
 import org.hibernate.spi.NavigablePath;
-import org.hibernate.sql.ast.tree.expression.JdbcParameter;
 import org.hibernate.sql.ast.tree.from.TableGroup;
 import org.hibernate.sql.ast.tree.select.QuerySpec;
 import org.hibernate.sql.ast.tree.select.SelectStatement;
 import org.hibernate.sql.exec.spi.JdbcParameterBindings;
 import org.hibernate.sql.exec.spi.JdbcParametersList;
-import org.hibernate.sql.results.graph.DomainResult;
 import org.hibernate.sql.results.graph.entity.LoadingEntityEntry;
-import org.hibernate.sql.results.graph.entity.internal.EntityResultInitializer;
 
 /**
  * Encapsulates details related to entities which contain sub-select-fetchable
@@ -151,8 +148,7 @@ private StandardRegistrationHandler(
 
 		public void addKey(EntityKey key, LoadingEntityEntry entry) {
 			if ( batchFetchQueue.getSession().getLoadQueryInfluencers()
-						.hasSubselectLoadableCollections( entry.getDescriptor() )
-					&& shouldAddSubselectFetch( entry ) ) {
+					.hasSubselectLoadableCollections( entry.getDescriptor() ) ) {
 				final SubselectFetch subselectFetch = subselectFetches.computeIfAbsent(
 						entry.getEntityInitializer().getNavigablePath(),
 						navigablePath -> new SubselectFetch(
@@ -169,23 +165,5 @@ && shouldAddSubselectFetch( entry ) ) {
 				batchFetchQueue.addSubselect( key, subselectFetch );
 			}
 		}
-
-		private boolean shouldAddSubselectFetch(LoadingEntityEntry entry) {
-			if ( entry.getEntityInitializer() instanceof EntityResultInitializer ) {
-				return true;
-			}
-			else {
-				final NavigablePath entityInitializerParent = entry.getEntityInitializer().getNavigablePath().getParent();
-
-				// We want to add only the collections of the loading entities
-				for ( DomainResult<?> domainResult : loadingSqlAst.getDomainResultDescriptors() ) {
-					if ( domainResult.getNavigablePath().equals( entityInitializerParent ) ) {
-						return true;
-					}
-				}
-
-				return false;
-			}
-		}
 	}
 }

hibernate-core/src/main/java/org/hibernate/sql/exec/spi/ExecutionContext.java

@@ -60,10 +60,22 @@ default EntityMappingType getRootEntityDescriptor() {
 		return null;
 	}
 
+	/**
+	 *
+	 * @param entityKey
+	 * @param entry
+	 *
+	 * @deprecated use {@link #registerSubselect(EntityKey, LoadingEntityEntry)} instead.
+	 */
+	@Deprecated
 	default void registerLoadingEntityEntry(EntityKey entityKey, LoadingEntityEntry entry) {
 		// by default do nothing
 	}
 
+	default void registerSubselect(EntityKey entityKey, LoadingEntityEntry entry) {
+		registerLoadingEntityEntry( entityKey, entry );
+	}
+
 	/**
 	 * Hook to allow delaying calls to {@link LogicalConnectionImplementor#afterStatement()}.
 	 * Mainly used in the case of batching and multi-table mutations

hibernate-core/src/main/java/org/hibernate/sql/results/graph/embeddable/internal/NestedRowProcessingState.java

@@ -8,6 +8,7 @@
 
 import org.hibernate.engine.spi.CollectionKey;
 import org.hibernate.engine.spi.EntityKey;
+import org.hibernate.engine.spi.SubselectFetch;
 import org.hibernate.metamodel.mapping.EntityMappingType;
 import org.hibernate.query.spi.QueryOptions;
 import org.hibernate.query.spi.QueryParameterBindings;

hibernate-core/src/main/java/org/hibernate/sql/results/internal/StandardRowReader.java

@@ -83,7 +83,6 @@ public InitializersList getInitializersList() {
 	@Override
 	public T readRow(RowProcessingState rowProcessingState, JdbcValuesSourceProcessingOptions options) {
 		LoadingLogger.LOGGER.trace( "StandardRowReader#readRow" );
-
 		coordinateInitializers( rowProcessingState );
 
 		final Object[] resultRow = new Object[ assemblerCount ];
@@ -112,6 +111,7 @@ private void coordinateInitializers(RowProcessingState rowProcessingState) {
 
 	@Override
 	public void finishUp(JdbcValuesSourceProcessingState processingState) {
+		processingState.registerSubselect();
 		initializers.endLoading( processingState.getExecutionContext() );
 	}
 

hibernate-core/src/main/java/org/hibernate/sql/results/jdbc/internal/JdbcValuesSourceProcessingStateStandardImpl.java

@@ -20,6 +20,8 @@
 import org.hibernate.event.spi.PostLoadEvent;
 import org.hibernate.event.spi.PostLoadEventListener;
 import org.hibernate.event.spi.PreLoadEvent;
+import org.hibernate.internal.CoreLogging;
+import org.hibernate.internal.CoreMessageLogger;
 import org.hibernate.query.spi.QueryOptions;
 import org.hibernate.sql.exec.spi.Callback;
 import org.hibernate.sql.exec.spi.ExecutionContext;
@@ -36,6 +38,8 @@
  */
 public class JdbcValuesSourceProcessingStateStandardImpl implements JdbcValuesSourceProcessingState {
 
+	private static final CoreMessageLogger LOG = CoreLogging.messageLogger( JdbcValuesSourceProcessingStateStandardImpl.class );
+
 	private final ExecutionContext executionContext;
 	private final JdbcValuesSourceProcessingOptions processingOptions;
 
@@ -97,7 +101,6 @@ public void registerLoadingEntity(
 		if ( loadingEntityMap == null ) {
 			loadingEntityMap = new HashMap<>();
 		}
-		executionContext.registerLoadingEntityEntry( entityKey, loadingEntry );
 		loadingEntityMap.put( entityKey, loadingEntry );
 	}
 
@@ -137,6 +140,22 @@ public LoadingCollectionEntry findLoadingCollectionLocally(CollectionKey key) {
 		return loadingCollectionMap.get( key );
 	}
 
+	@Override
+	public void registerSubselect() {
+		if ( loadingEntityMap != null && loadingEntityMap.size() > 1 ) {
+			loadingEntityMap.forEach(
+					(entityKey, loadingEntityEntry) ->
+							executionContext.registerSubselect( entityKey, loadingEntityEntry )
+			);
+		}
+		else {
+			LOG.tracef(
+					"Skipping create subselects because there are fewer than 2 results, so query by key is more efficient.",
+					getClass().getName()
+			);
+		}
+	}
+
 	@Override
 	public void registerLoadingCollection(CollectionKey key, LoadingCollectionEntry loadingCollectionEntry) {
 		if ( loadingCollectionMap == null ) {

hibernate-core/src/main/java/org/hibernate/sql/results/jdbc/spi/JdbcValuesSourceProcessingState.java

@@ -80,5 +80,8 @@ void registerLoadingCollection(
 			CollectionKey collectionKey,
 			LoadingCollectionEntry loadingCollectionEntry);
 
+	default void registerSubselect() {
+	}
+
 	void finishUp();
 }

hibernate-core/src/test/java/org/hibernate/orm/test/mapping/fetch/depth/DepthOneBatchTest.java

@@ -104,7 +104,7 @@ public void tesGetAgency(SessionFactoryScope scope) {
 					);
 
 					assertThat( executedQueries.get( 4 ).toLowerCase() ).isEqualTo(
-							"select u1_0.group_id,u1_1.user_id,a1_0.agency_id,a1_0.agency_txt,u1_1.user_name from group_user u1_0 join user_table u1_1 on u1_1.user_id=u1_0.user_id left join agency_table a1_0 on a1_0.agency_id=u1_1.agency_id where u1_0.group_id in (select g1_0.group_id from group_table g1_0 where g1_0.agency_id=?)"
+							"select u1_0.group_id,u1_1.user_id,a1_0.agency_id,a1_0.agency_txt,u1_1.user_name from group_user u1_0 join user_table u1_1 on u1_1.user_id=u1_0.user_id left join agency_table a1_0 on a1_0.agency_id=u1_1.agency_id where u1_0.group_id=?"
 					);
 
 				}

hibernate-core/src/test/java/org/hibernate/orm/test/mapping/fetch/depth/DepthOneTest.java

@@ -100,7 +100,7 @@ public void tesGetAgency(SessionFactoryScope scope) {
 					);
 
 					assertThat( executedQueries.get( 3 ).toLowerCase() ).isEqualTo(
-							"select u1_0.group_id,u1_1.user_id,a1_0.agency_id,a1_0.agency_txt,u1_1.user_name from group_user u1_0 join user_table u1_1 on u1_1.user_id=u1_0.user_id left join agency_table a1_0 on a1_0.agency_id=u1_1.agency_id where u1_0.group_id in (select g1_0.group_id from group_table g1_0 where g1_0.agency_id=?)"
+							"select u1_0.group_id,u1_1.user_id,a1_0.agency_id,a1_0.agency_txt,u1_1.user_name from group_user u1_0 join user_table u1_1 on u1_1.user_id=u1_0.user_id left join agency_table a1_0 on a1_0.agency_id=u1_1.agency_id where u1_0.group_id=?"
 					);
 
 					assertThat( executedQueries.get( 4 ).toLowerCase() ).isEqualTo(

hibernate-core/src/test/java/org/hibernate/orm/test/mapping/fetch/subselect/SubselectOneToManyTest.java

@@ -109,7 +109,7 @@ public void testShouldJoin(SessionFactoryScope scope) {
 			assertThat( parent.getChildren() ).hasSize( 2 );
 			statementInspector.assertExecutedCount( 3 ); // 1 query for parent, 1 for grandparent, 1 for children
 			statementInspector.assertNumberOfOccurrenceInQuery( 0, "join", 1 );
-			statementInspector.assertNumberOfOccurrenceInQuery( 2, "join", 1 );
+			statementInspector.assertNumberOfOccurrenceInQuery( 2, "join", 0 );
 		} );
 	}