GH-175 - More defensive auto-configuration of MongoDB transactions.

We now opt out of defining bean definitions for MongoTransactionManager and TransactionTemplate if user defined. We also make sure to run before the EnableTransactionManagementConfiguration to make sure that will see our auto-configured MongoTransactionManager.

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

@@ -16,7 +16,10 @@
 package org.springframework.modulith.events.mongodb;
 
 import org.springframework.boot.autoconfigure.AutoConfiguration;
+import org.springframework.boot.autoconfigure.AutoConfigureBefore;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
+import org.springframework.boot.autoconfigure.transaction.TransactionAutoConfiguration;
 import org.springframework.context.annotation.Bean;
 import org.springframework.data.mongodb.MongoDatabaseFactory;
 import org.springframework.data.mongodb.MongoTransactionManager;
@@ -31,6 +34,7 @@ import org.springframework.transaction.support.TransactionTemplate;
  * @author Oliver Drotbohm
  */
 @AutoConfiguration
+@AutoConfigureBefore(TransactionAutoConfiguration.class)
 @ConditionalOnProperty(//
 		name = "spring.modulith.events.mongobd.transaction-management.enabled",
 		havingValue = "true",
@@ -38,11 +42,13 @@ import org.springframework.transaction.support.TransactionTemplate;
 class MongoDbTransactionAutoConfiguration {
 
 	@Bean
+	@ConditionalOnMissingBean
 	MongoTransactionManager transactionManager(MongoDatabaseFactory factory) {
 		return new MongoTransactionManager(factory);
 	}
 
 	@Bean
+	@ConditionalOnMissingBean
 	TransactionTemplate transactionTemplate(PlatformTransactionManager txManager) {
 		return new TransactionTemplate(txManager);
 	}