GH-175 - Auto-configure transactions for MongoDB by default.

As the Event Publication registry only works in transactional environments, we should enable them for MongoDB by default. This will require a replica setup for the MongoDB instance the application interacts with.

spring-modulith-events/spring-modulith-events-mongodb/src/main/java/org/springframework/modulith/events/mongodb/MongoDbTransactionAutoConfiguration.java

@@ -0,0 +1,49 @@
+/*
+ * Copyright 2023 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.modulith.events.mongodb;
+
+import org.springframework.boot.autoconfigure.AutoConfiguration;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
+import org.springframework.context.annotation.Bean;
+import org.springframework.data.mongodb.MongoDatabaseFactory;
+import org.springframework.data.mongodb.MongoTransactionManager;
+import org.springframework.modulith.events.EventPublicationRegistry;
+import org.springframework.transaction.PlatformTransactionManager;
+import org.springframework.transaction.support.TransactionTemplate;
+
+/**
+ * Auto-configuration to enable MongoDB transaction management as that is required for the
+ * {@link EventPublicationRegistry} to work properly.
+ *
+ * @author Oliver Drotbohm
+ */
+@AutoConfiguration
+@ConditionalOnProperty(//
+		name = "spring.modulith.events.mongobd.transaction-management.enabled",
+		havingValue = "true",
+		matchIfMissing = true)
+class MongoDbTransactionAutoConfiguration {
+
+	@Bean
+	MongoTransactionManager transactionManager(MongoDatabaseFactory factory) {
+		return new MongoTransactionManager(factory);
+	}
+
+	@Bean
+	TransactionTemplate transactionTemplate(PlatformTransactionManager txManager) {
+		return new TransactionTemplate(txManager);
+	}
+}

spring-modulith-events/spring-modulith-events-mongodb/src/main/resources/META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports

@@ -1 +1,2 @@
 org.springframework.modulith.events.mongodb.MongoDbEventPublicationAutoConfiguration
+org.springframework.modulith.events.mongodb.MongoDbTransactionAutoConfiguration

spring-modulith-events/spring-modulith-events-mongodb/src/test/java/org/springframework/modulith/events/mongodb/MongoDbEventPublicationAutoConfigurationIntegrationTests.java

@@ -21,6 +21,7 @@ import org.junit.jupiter.api.Test;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.test.context.SpringBootTest;
 import org.springframework.context.ApplicationContext;
+import org.springframework.data.mongodb.MongoTransactionManager;
 import org.springframework.modulith.events.EventPublicationRegistry;
 import org.springframework.modulith.testapp.TestApplication;
 
@@ -34,10 +35,11 @@ class MongoDbEventPublicationAutoConfigurationIntegrationTests {
 
 	@Autowired ApplicationContext context;
 
-	@Test // GH-4
+	@Test // GH-4, GH-175
 	void bootstrapsApplicationComponents() {
 
 		assertThat(context.getBean(EventPublicationRegistry.class)).isNotNull();
 		assertThat(context.getBean(MongoDbEventPublicationRepository.class)).isNotNull();
+		assertThat(context.getBean(MongoTransactionManager.class)).isNotNull();
 	}
 }

src/docs/asciidoc/40-events.adoc

@@ -147,8 +147,11 @@ To ease that task, Spring Modulith provides starter POMs that are centered aroun
 The following starters are available:
 
 * `spring-modulith-starter-jpa` -- Using JPA as persistence technology.
-* `spring-modulith-starter-jdbc` -- Using JDBC as persistence technology. Also works in JPA-based applications but bypasses your JPA provider for actual event persistence.
+* `spring-modulith-starter-jdbc` -- Using JDBC as persistence technology.
+Also works in JPA-based applications but bypasses your JPA provider for actual event persistence.
 * `spring-modulith-starter-mongodb` -- Using MongoDB behind Spring Data MongoDB.
+Also enables MongoDB transactions and requires a replica set setup of the server to interact with.
+The transaction auto-configuration can be disabled by setting the `spring.modulith.events.mongobd.transaction-management.enabled` property to `false`.
 
 [[events.integration-testing]]
 == Integration Testing Application Modules Working with Events