Support fror @Inject StatelessSession

Why:

 * Sometimes you just want to do raw data access

This change addreses the need by:

 * Add StatelessSession as a possible injection.

Signed-off-by: Max Rydahl Andersen <manderse@redhat.com>

docs/src/main/asciidoc/hibernate-orm.adoc

@@ -139,6 +139,36 @@ WARNING: Make sure to wrap methods modifying your database (e.g. `entity.persist
 CDI bean method `@Transactional` will do that for you and make that method a transaction boundary. We recommend doing
 so at your application entry point boundaries like your REST endpoint controllers.
 
+=== Processing raw or large amount of data
+
+`StatelessSession` are supported too and can be injected and used standalone or inter-mixed with your `EntityManager`.
+The benefits of `StatelessSession` are that entities are not put in a session-level cache, allowing for more raw and in some cases higher performance
+data access. Especially useful when reading/processing large amount of data.
+
+[source,java]
+.Example application bean using Hibernate
+--
+@ApplicationScoped
+public class SantaClausService {
+@Inject
+StatelessSession session; <.>
+
+    @Transactional
+    public void queryGifts(String giftDescription) {
+        ScrollableResults gifts = session.getQuery("from Gift")
+        .scroll(ScrollMode.FORWARD_ONLY); <.>
+        while ( gifts.next() ) {
+            Gift gift = (Gift) gifts.get(0);
+            gift.updateStuff(...);
+            session.update(customer); <.>
+        }
+    }
+}
+--
+<.> Inject your stateless session and have fun; it will open or reuse the active transaction.
+<.> Using `scroll()` means you can process the data without loading the complete resultset or list of data in memory.
+<.> Since using a stateless session you need to explicitly call `update()` to save changes.
+
 [[hibernate-configuration-properties]]
 === Hibernate ORM configuration properties
 

extensions/hibernate-orm/deployment/src/main/java/io/quarkus/hibernate/orm/deployment/HibernateOrmProcessor.java

@@ -95,6 +95,7 @@
 import io.quarkus.hibernate.orm.deployment.integration.HibernateOrmIntegrationRuntimeConfiguredBuildItem;
 import io.quarkus.hibernate.orm.runtime.DefaultEntityManagerFactoryProducer;
 import io.quarkus.hibernate.orm.runtime.DefaultEntityManagerProducer;
+import io.quarkus.hibernate.orm.runtime.DefaultStatelessSessionProducer;
 import io.quarkus.hibernate.orm.runtime.HibernateOrmRecorder;
 import io.quarkus.hibernate.orm.runtime.JPAConfig;
 import io.quarkus.hibernate.orm.runtime.JPAResourceReferenceProvider;
@@ -421,6 +422,7 @@ void registerBeans(BuildProducer<AdditionalBeanBuildItem> additionalBeans, Combi
             if (isUserDefinedProducerMissing(combinedIndex.getIndex(), PERSISTENCE_CONTEXT)) {
                 additionalBeans.produce(new AdditionalBeanBuildItem(DefaultEntityManagerProducer.class));
             }
+            additionalBeans.produce(new AdditionalBeanBuildItem(DefaultStatelessSessionProducer.class));
         }
     }
 

extensions/hibernate-orm/deployment/src/test/java/io/quarkus/hibernate/orm/StatelessSessionTest.java

@@ -0,0 +1,46 @@
+package io.quarkus.hibernate.orm;
+
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+
+import java.util.List;
+
+import javax.inject.Inject;
+
+import org.hibernate.StatelessSession;
+import org.jboss.shrinkwrap.api.ShrinkWrap;
+import org.jboss.shrinkwrap.api.spec.JavaArchive;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.RegisterExtension;
+
+import io.quarkus.arc.Arc;
+import io.quarkus.hibernate.orm.enhancer.Address;
+import io.quarkus.test.QuarkusUnitTest;
+
+/**
+ * @author Max Rydahl Andersen <manderse@redhat.com>
+ */
+public class StatelessSessionTest {
+
+    @RegisterExtension
+    static QuarkusUnitTest runner = new QuarkusUnitTest()
+            .setArchiveProducer(() -> ShrinkWrap.create(JavaArchive.class)
+                    .addClass(Address.class)
+                    .addAsResource("application.properties"));
+
+    @Inject
+    StatelessSession statelessSession;
+
+    @Test
+    public void testStatelessSession() {
+        Arc.container().requestContext().activate();
+        try {
+            List list = statelessSession.createNativeQuery("SELECT VALUE FROM INFORMATION_SCHEMA.SETTINGS")
+                    .addScalar("VALUE")
+                    .list();
+            assertNotNull(list);
+        } finally {
+            Arc.container().requestContext().terminate();
+        }
+    }
+
+}

extensions/hibernate-orm/runtime/src/main/java/io/quarkus/hibernate/orm/runtime/DefaultStatelessSessionProducer.java

@@ -0,0 +1,22 @@
+package io.quarkus.hibernate.orm.runtime;
+
+import javax.enterprise.inject.Produces;
+import javax.inject.Inject;
+import javax.inject.Singleton;
+import javax.persistence.EntityManagerFactory;
+
+import org.hibernate.SessionFactory;
+import org.hibernate.StatelessSession;
+
+public class DefaultStatelessSessionProducer {
+
+    @Inject
+    EntityManagerFactory em;
+
+    @Produces
+    @Singleton
+    StatelessSession produceStatelessSession() {
+        return em.unwrap(SessionFactory.class).openStatelessSession();
+    }
+
+}

extensions/hibernate-orm/runtime/src/main/java/io/quarkus/hibernate/orm/runtime/JPAResourceReferenceProvider.java

@@ -9,6 +9,8 @@
 import javax.persistence.PersistenceContext;
 import javax.persistence.PersistenceUnit;
 
+import org.hibernate.StatelessSession;
+
 import io.quarkus.arc.Arc;
 import io.quarkus.arc.InstanceHandle;
 import io.quarkus.arc.ResourceReferenceProvider;
@@ -56,8 +58,39 @@ public void destroy() {
                     };
                 }
             }
-        }
+        } else if (StatelessSession.class.equals(type)) {
+            PersistenceContext pc = getAnnotation(annotations, PersistenceContext.class);
+            if (pc != null) {
+                if (jpaConfig.isJtaEnabled()) {
+                    TransactionEntityManagers transactionEntityManagers = Arc.container()
+                            .instance(TransactionEntityManagers.class).get();
+                    ForwardingEntityManager entityManager = new ForwardingEntityManager() {
 
+                        @Override
+                        protected EntityManager delegate() {
+                            return transactionEntityManagers.getEntityManager(pc.unitName());
+                        }
+                    };
+                    return () -> entityManager;
+                } else {
+                    EntityManagerFactory entityManagerFactory = jpaConfig.getEntityManagerFactory(pc.unitName());
+                    EntityManager entityManager = entityManagerFactory.createEntityManager();
+                    return new InstanceHandle<Object>() {
+
+                        @Override
+                        public Object get() {
+                            return entityManager;
+                        }
+
+                        @Override
+                        public void destroy() {
+                            entityManager.close();
+                        }
+                    };
+                }
+            }
+
+        }
         return null;
     }