Allow accessing the MongoDB ClientSession programmatively

docs/src/main/asciidoc/mongodb-panache.adoc

@@ -770,6 +770,8 @@ MongoDB offers ACID transactions since version 4.0.
 
 To use them with MongoDB with Panache you need to annotate the method that starts the transaction with the `@Transactional` annotation.
 
+Inside methods annotated with `@Transactional` you can access the `ClientSession` with `Panache.getClientSession()` if needed.
+
 In MongoDB, a transaction is only possible on a replicaset,
 luckily our xref:mongodb.adoc#dev-services[Dev Services for MongoDB] setups a single node replicaset so it is compatible with transactions.
 

extensions/panache/mongodb-panache-common/runtime/src/main/java/io/quarkus/mongodb/panache/common/runtime/MongoOperations.java

@@ -333,23 +333,27 @@ ClientSession getSession(Object entity) {
         return getSession(entity.getClass());
     }
 
-    ClientSession getSession(Class<?> entityClass) {
+    public ClientSession getSession(Class<?> entityClass) {
         ClientSession clientSession = null;
-        MongoEntity mongoEntity = entityClass.getAnnotation(MongoEntity.class);
         InstanceHandle<TransactionSynchronizationRegistry> instance = Arc.container()
                 .instance(TransactionSynchronizationRegistry.class);
         if (instance.isAvailable()) {
             TransactionSynchronizationRegistry registry = instance.get();
             if (registry.getTransactionStatus() == Status.STATUS_ACTIVE) {
                 clientSession = (ClientSession) registry.getResource(SESSION_KEY);
                 if (clientSession == null) {
+                    MongoEntity mongoEntity = entityClass == null ? null : entityClass.getAnnotation(MongoEntity.class);
                     return registerClientSession(mongoEntity, registry);
                 }
             }
         }
         return clientSession;
     }
 
+    public ClientSession getSession() {
+        return getSession(null);
+    }
+
     private ClientSession registerClientSession(MongoEntity mongoEntity,
             TransactionSynchronizationRegistry registry) {
         TransactionManager transactionManager = Arc.container().instance(TransactionManager.class).get();

extensions/panache/mongodb-panache-kotlin/runtime/src/main/kotlin/io/quarkus/mongodb/panache/kotlin/Panache.kt

@@ -0,0 +1,27 @@
+package io.quarkus.mongodb.panache.kotlin
+
+import com.mongodb.session.ClientSession
+import io.quarkus.mongodb.panache.kotlin.runtime.KotlinMongoOperations
+
+object Panache {
+    /**
+     * Access the current MongoDB ClientSession from the transaction context. Can be used inside a
+     * method annotated with `@Transactional` to manually access the client session.
+     *
+     * @return ClientSession or null if not in the context of a transaction.
+     */
+    val session: ClientSession
+        get() = KotlinMongoOperations.INSTANCE.session
+
+    /**
+     * Access the current MongoDB ClientSession from the transaction context.
+     *
+     * @param entityClass the class of the MongoDB entity in case it is configured to use the
+     *   non-default client.
+     * @return ClientSession or null if not in the context of a transaction.
+     * @see [session]
+     */
+    fun getSession(entityClass: Class<*>?): ClientSession {
+        return KotlinMongoOperations.INSTANCE.getSession(entityClass)
+    }
+}

extensions/panache/mongodb-panache/runtime/src/main/java/io/quarkus/mongodb/panache/Panache.java

@@ -0,0 +1,30 @@
+package io.quarkus.mongodb.panache;
+
+import com.mongodb.session.ClientSession;
+
+import io.quarkus.mongodb.panache.runtime.JavaMongoOperations;
+
+public class Panache {
+
+    /**
+     * Access the current MongoDB ClientSession from the transaction context.
+     * Can be used inside a method annotated with `@Transactional` to manually access the client session.
+     *
+     * @return ClientSession or null if not in the context of a transaction.
+     */
+    public static ClientSession getSession() {
+        return JavaMongoOperations.INSTANCE.getSession();
+    }
+
+    /**
+     * Access the current MongoDB ClientSession from the transaction context.
+     *
+     * @see #getSession()
+     *
+     * @param entityClass the class of the MongoDB entity in case it is configured to use the non-default client.
+     * @return ClientSession or null if not in the context of a transaction.
+     */
+    public static ClientSession getSession(Class<?> entityClass) {
+        return JavaMongoOperations.INSTANCE.getSession(entityClass);
+    }
+}

integration-tests/mongodb-panache/src/main/java/io/quarkus/it/mongodb/panache/transaction/TransactionPersonResource.java

@@ -1,5 +1,7 @@
 package io.quarkus.it.mongodb.panache.transaction;
 
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+
 import java.net.URI;
 import java.util.ArrayList;
 import java.util.List;
@@ -14,6 +16,7 @@
 
 import com.mongodb.client.MongoClient;
 
+import io.quarkus.mongodb.panache.Panache;
 import io.quarkus.runtime.StartupEvent;
 
 @Path("/transaction")
@@ -42,6 +45,7 @@ public List<TransactionPerson> getPersons() {
     @Transactional
     public Response addPerson(TransactionPerson person) {
         person.persist();
+        assertNotNull(Panache.getSession(TransactionPerson.class));
         return Response.created(URI.create("/transaction/" + person.id.toString())).build();
     }