How to implement spring data mongo multidatabase transactions - spring

Question

I created an application that copies data from one database to another one based on this tutorial.
In fact, I need to make a method that inserts in two different databases transactional.
Is this possible with MongoDB ? and how can I implement it?

Answer 1

To use multi-document transactions in MongoDB across multiple databases in Spring Data MongoDB, you need to configure a MongoTemplate per database, but all of them must use the same MongoDbFactory because it is treated as the transactional resource.
This means that you will need to override a couple of methods of MongoTemplate to make it use the database it should use (and not the one configured inside SimpleMongoClientDbFactory).
Let's assume that your databases are called 'one' and 'two'. Then it goes like this:
public class MongoTemplateWithFixedDatabase extends MongoTemplate {
private final MongoDbFactory mongoDbFactory;
private final String databaseName;
public MongoTemplateWithFixedDatabase(MongoDbFactory mongoDbFactory,
MappingMongoConverter mappingMongoConverter, String databaseName) {
super(mongoDbFactory, mappingMongoConverter);
this.mongoDbFactory = mongoDbFactory;
this.databaseName = databaseName;
}
#Override
protected MongoDatabase doGetDatabase() {
return MongoDatabaseUtils.getDatabase(databaseName, mongoDbFactory, ON_ACTUAL_TRANSACTION);
}
}
and
#Bean
public MongoDbFactory mongoDbFactory() {
// here, some 'default' database name is configured, the following MongoTemplate instances will ignore it
return new SimpleMongoDbFactory(mongoClient(), getDatabaseName());
}
#Bean
public MongoTransactionManager mongoTransactionManager() {
return new MongoTransactionManager(mongoDbFactory());
}
#Bean
public MongoTemplate mongoTemplateOne(MongoDbFactory mongoDbFactory,
MappingMongoConverter mappingMongoConverter) {
MongoTemplate template = new MongoTemplateWithFixedDatabase(mongoDbFactory,
mappingMongoConverter, "one");
return template;
}
#Bean
public MongoTemplate mongoTemplateTwo(MongoDbFactory mongoDbFactory,
MappingMongoConverter mappingMongoConverter) {
MongoTemplate template = new MongoTemplateWithFixedDatabase(mongoDbFactory,
mappingMongoConverter, "two");
return template;
}
Then just inject mongoTemplateOne and mongoTemplateTwo in your service, mark its method with #Transactional and it should work.
Reactive case
In the reactive case, it's very similar. Of course, you need to use reactive versions of the classes like ReactiveMongoTemplate, ReactiveMongoDatabaseFactory, ReactiveMongoTransactionManager.
There is also a couple of caveats. First, you have to override 3 methods, not 2 (as getCollection(String) also needs to be overridden). Also, I had to do it with an abstract class to make it work:
#Bean
public ReactiveMongoOperations reactiveMongoTemplateOne(
#ReactiveMongoDatabaseFactory reactiveMongoDatabaseFactory,
MappingMongoConverter mappingMongoConverter) {
ReactiveMongoTemplate template = new ReactiveMongoTemplate(reactiveMongoDatabaseFactory,
mappingMongoConverter) {
#Override
protected Mono<MongoDatabase> doGetDatabase() {
return ReactiveMongoDatabaseUtils.getDatabase("one", reactiveMongoDatabaseFactory,
ON_ACTUAL_TRANSACTION);
}
#Override
public MongoDatabase getMongoDatabase() {
return reactiveMongoDatabaseFactory.getMongoDatabase(getDatabaseName());
}
#Override
public MongoCollection<Document> getCollection(String collectionName) {
Assert.notNull(collectionName, "Collection name must not be null!");
try {
return reactiveMongoDatabaseFactory.getMongoDatabase(getDatabaseName())
.getCollection(collectionName);
} catch (RuntimeException e) {
throw potentiallyConvertRuntimeException(e,
reactiveMongoDatabaseFactory.getExceptionTranslator());
}
}
private RuntimeException potentiallyConvertRuntimeException(RuntimeException ex,
PersistenceExceptionTranslator exceptionTranslator) {
RuntimeException resolved = exceptionTranslator.translateExceptionIfPossible(ex);
return resolved == null ? ex : resolved;
}
};
return template;
}
P.S. the provided code was tested with spring-data-mongodb 2.2.4.