Transaction support for MongoDB with Panache

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

@@ -656,7 +656,14 @@ quarkus.log.category."io.quarkus.mongodb.panache.runtime".level=DEBUG
 
 == Transactions
 
-WARNING: MongoDB offers ACID transactions since version 4.0. MongoDB with Panache doesn't provide support for them.
+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.
+
+Transactions can be configured via the `@MongoTransactionConfiguration` that allows to specify the read preference, read concern,
+ and write concern used during the lifespan of the transaction.
+
+WARNING: Transaction support inside MongoDB with Panache is still experimental.
 
 == Custom IDs
 
@@ -890,6 +897,8 @@ public Multi<ReactivePerson> streamPersons() {
 
 TIP: `@SseElementType(MediaType.APPLICATION_JSON)` tells RESTEasy to serialize the object in JSON.
 
+WARNING: Transactions are not supported for Reactive Entities and Repositories.
+
 == Mocking
 
 === Using the active-record pattern

extensions/panache/mongodb-panache-common/deployment/pom.xml

@@ -37,6 +37,10 @@
             <groupId>io.quarkus</groupId>
             <artifactId>quarkus-mongodb-panache-common</artifactId>
         </dependency>
+        <dependency>
+            <groupId>io.quarkus</groupId>
+            <artifactId>quarkus-narayana-jta-deployment</artifactId>
+        </dependency>
 
         <dependency>
             <groupId>io.quarkus</groupId>

extensions/panache/mongodb-panache-common/runtime/pom.xml

@@ -43,6 +43,10 @@
             <artifactId>quarkus-jackson</artifactId>
             <optional>true</optional>
         </dependency>
+        <dependency>
+            <groupId>io.quarkus</groupId>
+            <artifactId>quarkus-narayana-jta</artifactId>
+        </dependency>
         <dependency>
             <groupId>org.junit.jupiter</groupId>
             <artifactId>junit-jupiter</artifactId>

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

@@ -6,10 +6,12 @@
 import java.util.Set;
 import java.util.stream.Stream;
 
+import org.bson.BsonDocument;
 import org.bson.Document;
 import org.bson.conversions.Bson;
 
 import com.mongodb.ReadPreference;
+import com.mongodb.client.ClientSession;
 import com.mongodb.client.FindIterable;
 import com.mongodb.client.MongoCollection;
 import com.mongodb.client.MongoCursor;
@@ -21,6 +23,7 @@
 
 public class CommonPanacheQueryImpl<Entity> {
     private MongoCollection collection;
+    private ClientSession clientSession;
     private Bson mongoQuery;
     private Bson sort;
     private Bson projections;
@@ -32,14 +35,17 @@ public class CommonPanacheQueryImpl<Entity> {
 
     private Collation collation;
 
-    public CommonPanacheQueryImpl(MongoCollection<? extends Entity> collection, Bson mongoQuery, Bson sort) {
+    public CommonPanacheQueryImpl(MongoCollection<? extends Entity> collection, ClientSession session, Bson mongoQuery,
+            Bson sort) {
         this.collection = collection;
+        this.clientSession = session;
         this.mongoQuery = mongoQuery;
         this.sort = sort;
     }
 
     private CommonPanacheQueryImpl(CommonPanacheQueryImpl<?> previousQuery, Bson projections, Class<?> documentClass) {
         this.collection = previousQuery.collection.withDocumentClass(documentClass);
+        this.clientSession = previousQuery.clientSession;
         this.mongoQuery = previousQuery.mongoQuery;
         this.sort = previousQuery.sort;
         this.projections = projections;
@@ -150,7 +156,8 @@ public <T extends Entity> CommonPanacheQueryImpl<T> withReadPreference(ReadPrefe
     @SuppressWarnings("unchecked")
     public long count() {
         if (count == null) {
-            count = collection.countDocuments(mongoQuery);
+            Bson query = getQuery();
+            count = clientSession == null ? collection.countDocuments(query) : collection.countDocuments(clientSession, query);
         }
         return count;
     }
@@ -162,23 +169,21 @@ public <T extends Entity> List<T> list() {
     @SuppressWarnings("unchecked")
     private <T extends Entity> List<T> list(Integer limit) {
         List<T> list = new ArrayList<>();
-        FindIterable find = mongoQuery == null ? collection.find() : collection.find(mongoQuery);
+        Bson query = getQuery();
+        FindIterable find = clientSession == null ? collection.find(query) : collection.find(clientSession, query);
         if (this.projections != null) {
             find.projection(projections);
         }
         if (this.collation != null) {
             find.collation(collation);
         }
         manageOffsets(find, limit);
-        MongoCursor<T> cursor = find.sort(sort).iterator();
 
-        try {
+        try (MongoCursor<T> cursor = find.sort(sort).iterator()) {
             while (cursor.hasNext()) {
                 T entity = cursor.next();
                 list.add(entity);
             }
-        } finally {
-            cursor.close();
         }
         return list;
     }
@@ -232,4 +237,8 @@ private void manageOffsets(FindIterable find, Integer limit) {
             find.limit(limit);
         }
     }
+
+    private Bson getQuery() {
+        return mongoQuery == null ? new BsonDocument() : mongoQuery;
+    }
 }