HHH-19849 Add an SPI that allows attaching session-scoped "extensions" to the session/statelesssession implementors

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

@@ -0,0 +1,18 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ * Copyright Red Hat Inc. and Hibernate Authors
+ */
+package org.hibernate.engine.spi;
+
+import org.hibernate.Incubating;
+
+import java.util.function.Supplier;
+
+/**
+ * Marker interface for extensions to register themselves within a session instance.
+ *
+ * @see SharedSessionContractImplementor#getExtensionStorage(Class, Supplier)
+ */
+@Incubating
+public interface ExtensionStorage {
+}

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

@@ -75,6 +75,7 @@
 import java.util.Set;
 import java.util.TimeZone;
 import java.util.UUID;
+import java.util.function.Supplier;
 
 /**
  * A wrapper class that delegates all method invocations to a delegate instance of
@@ -517,6 +518,11 @@ public RootGraphImplementor<?> getEntityGraph(String graphName) {
 		return delegate.getEntityGraph( graphName );
 	}
 
+	@Override
+	public <T extends ExtensionStorage> T getExtensionStorage(Class<T> extension, Supplier<T> createIfMissing) {
+		return delegate.getExtensionStorage( extension, createIfMissing );
+	}
+
 	@Override
 	public <T> QueryImplementor<T> createQuery(CriteriaSelect<T> selectQuery) {
 		return delegate.createQuery( selectQuery );

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

@@ -6,6 +6,8 @@
 
 import java.util.Set;
 import java.util.UUID;
+import java.util.function.Supplier;
+
 import jakarta.persistence.TransactionRequiredException;
 import org.checkerframework.checker.nullness.qual.Nullable;
 
@@ -621,4 +623,16 @@ default boolean isStatelessSession() {
 
 	@Override
 	RootGraphImplementor<?> getEntityGraph(String graphName);
+
+	/**
+	 * Allows accessing session scoped extension storages of the particular session instance.
+	 *
+	 * @param extension The extension storage attached to the current session.
+	 * @param createIfMissing Creates a storage extension using the supplier,
+	 * if the current session does not yet have the particular storage type attached to this session.
+	 * @param <T> The type of the extension storage.
+	 */
+	@Incubating
+	<T extends ExtensionStorage> T getExtensionStorage(Class<T> extension, Supplier<T> createIfMissing);
+
 }

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

@@ -52,6 +52,7 @@
 import java.util.Set;
 import java.util.TimeZone;
 import java.util.UUID;
+import java.util.function.Supplier;
 
 /**
  * A wrapper class that delegates all method invocations to a delegate instance of
@@ -663,6 +664,11 @@ public RootGraphImplementor<?> getEntityGraph(String graphName) {
 		return delegate.getEntityGraph( graphName );
 	}
 
+	@Override
+	public <T extends ExtensionStorage> T getExtensionStorage(Class<T> extension, Supplier<T> createIfMissing) {
+		return delegate.getExtensionStorage( extension, createIfMissing );
+	}
+
 	@Override
 	public <T> List<EntityGraph<? super T>> getEntityGraphs(Class<T> entityClass) {
 		return delegate.getEntityGraphs( entityClass );

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

@@ -41,6 +41,7 @@
 import org.hibernate.engine.jdbc.spi.JdbcServices;
 import org.hibernate.engine.spi.EntityKey;
 import org.hibernate.engine.spi.ExceptionConverter;
+import org.hibernate.engine.spi.ExtensionStorage;
 import org.hibernate.engine.spi.LoadQueryInfluencers;
 import org.hibernate.engine.spi.SessionEventListenerManager;
 import org.hibernate.engine.spi.SessionFactoryImplementor;
@@ -111,12 +112,15 @@
 import java.io.Serial;
 import java.sql.Connection;
 import java.sql.SQLException;
+import java.util.HashMap;
 import java.util.List;
 import java.util.Locale;
+import java.util.Map;
 import java.util.Objects;
 import java.util.TimeZone;
 import java.util.UUID;
 import java.util.function.Function;
+import java.util.function.Supplier;
 
 import static java.lang.Boolean.TRUE;
 import static org.hibernate.boot.model.naming.Identifier.toIdentifier;
@@ -186,6 +190,8 @@ public abstract class AbstractSharedSessionContract implements SharedSessionCont
 	private transient ExceptionConverter exceptionConverter;
 	private transient SessionAssociationMarkers sessionAssociationMarkers;
 
+	private transient Map<Class<?>, Object> extensionStorages;
+
 	public AbstractSharedSessionContract(SessionFactoryImpl factory, SessionCreationOptions options) {
 		this.factory = factory;
 
@@ -1704,6 +1710,20 @@ public SessionAssociationMarkers getSessionAssociationMarkers() {
 		return sessionAssociationMarkers;
 	}
 
+	@Override
+	public <T extends ExtensionStorage> T getExtensionStorage(Class<T> extension, Supplier<T> createIfMissing) {
+		if ( extensionStorages == null ) {
+			extensionStorages = new HashMap<>();
+		}
+		Object storage = extensionStorages.get( extension );
+		if ( storage == null ) {
+			storage = createIfMissing.get();
+			extensionStorages.put( extension, storage );
+		}
+
+		return extension.cast( storage );
+	}
+
 	@Serial
 	private void writeObject(ObjectOutputStream oos) throws IOException {
 		SESSION_LOGGER.serializingSession( getSessionIdentifier() );

hibernate-core/src/test/java/org/hibernate/orm/test/engine/spi/SessionExtensionTest.java

@@ -0,0 +1,101 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ * Copyright Red Hat Inc. and Hibernate Authors
+ */
+package org.hibernate.orm.test.engine.spi;
+
+import jakarta.persistence.Id;
+import org.hibernate.engine.spi.ExtensionStorage;
+import org.hibernate.testing.orm.junit.DomainModel;
+import org.hibernate.testing.orm.junit.SessionFactory;
+import org.hibernate.testing.orm.junit.SessionFactoryScope;
+import org.junit.jupiter.api.Test;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+@DomainModel(annotatedClasses = {
+		SessionExtensionTest.UselessEntity.class,
+})
+@SessionFactory
+public class SessionExtensionTest {
+
+	@Test
+	public void failing(SessionFactoryScope scope) {
+		scope.inSession( sessionImplementor -> {
+			assertThatThrownBy(
+					() -> sessionImplementor.getExtensionStorage( MySometimesFailingExtensionStorage.class, MySometimesFailingExtensionStorage::new ) )
+					.isInstanceOf( UnsupportedOperationException.class );
+		} );
+
+		scope.inStatelessSession( sessionImplementor -> {
+			assertThatThrownBy(
+					() -> sessionImplementor.getExtensionStorage( MySometimesFailingExtensionStorage.class, MySometimesFailingExtensionStorage::new ) )
+					.isInstanceOf( UnsupportedOperationException.class );
+		} );
+	}
+
+	@Test
+	public void supplier(SessionFactoryScope scope) {
+		scope.inSession( sessionImplementor -> {
+			sessionImplementor.getExtensionStorage( MySometimesFailingExtensionStorage.class,
+							() -> new MySometimesFailingExtensionStorage( new HashMap<>() ) )
+					.add( new Extension( 1 ) );
+
+			assertThat( sessionImplementor.getExtensionStorage( MySometimesFailingExtensionStorage.class, MySometimesFailingExtensionStorage::new ).get( 1 ) )
+					.isNotNull()
+					.isEqualTo( new Extension( 1 ) );
+
+			assertThat( sessionImplementor.getExtensionStorage( MySometimesFailingExtensionStorage.class,
+					() -> new MySometimesFailingExtensionStorage( new HashMap<>() ) ).get( 1 ) )
+					.isNotNull()
+					.isEqualTo( new Extension( 1 ) );
+		} );
+
+		scope.inStatelessSession( sessionImplementor -> {
+			sessionImplementor.getExtensionStorage( MySometimesFailingExtensionStorage.class,
+							() -> new MySometimesFailingExtensionStorage( new HashMap<>() ) )
+					.add( new Extension( 1 ) );
+
+			assertThat( sessionImplementor.getExtensionStorage( MySometimesFailingExtensionStorage.class, MySometimesFailingExtensionStorage::new ).get( 1 ) )
+					.isNotNull()
+					.isEqualTo( new Extension( 1 ) );
+
+			assertThat( sessionImplementor.getExtensionStorage( MySometimesFailingExtensionStorage.class,
+					() -> new MySometimesFailingExtensionStorage( new HashMap<>() ) ).get( 1 ) )
+					.isNotNull()
+					.isEqualTo( new Extension( 1 ) );
+		} );
+	}
+
+	public static class MySometimesFailingExtensionStorage implements ExtensionStorage {
+		Map<Integer, Extension> extensions = new HashMap<>();
+
+		public MySometimesFailingExtensionStorage() {
+			throw new UnsupportedOperationException();
+		}
+
+		MySometimesFailingExtensionStorage(Map<Integer, Extension> extensions) {
+			this.extensions = extensions;
+		}
+
+		public void add(Extension extension) {
+			extensions.put( extension.number, extension );
+		}
+
+		public Extension get(int number) {
+			return extensions.get( number );
+		}
+	}
+
+	public record Extension(int number) {
+	}
+
+	static class UselessEntity {
+		@Id
+		Long id;
+	}
+}