MongoDB integration

MongoDB can be integrated by using the supplied MongoDB listeners from the barbelhisto-persistence-mongo package. Download the MongoDB listeners on Maven Central.

To register the listeners to BarbelHisto:

SimpleMongoListenerClient client = SimpleMongoListenerClient.create("mongodb://localhost:12345");
SimpleMongoLazyLoadingListener lazyloader = SimpleMongoLazyLoadingListener.create(client.getMongoClient(), "testDb", "testCol", DefaultPojo.class, BarbelHistoContext.getDefaultGson());
BarbelHisto<DefaultPojo> lazyHisto = BarbelHistoBuilder.barbel().withSynchronousEventListener(lazyloader).build();

To use BarbelHisto in conjunction with the listeners, applications should define an instance of BarbelHisto as singleton in their application. The singleton instance will be pre-fetched with data as it is required on retrieve or save operations performed by the client. Also, the listeners will save new versions automatically to the defined MongoCollection.

The simple listener implementations do not lock a document journal in the database. Therefore clients want to create a BarbelHisto singleton instance to ensure locking is performed properly on a document journal level. The simple listener implementations provide support for all BarbelQueries. If you define custom queries against BarbelHisto include the BarbelQueries.DOCUMENT_ID as a filter criterion.

Pessimistic locking

If you need multiple BarbelHisto instances access the document collection you can use the MongoPessimisticLockingListener to perform a pessimistic locking. This way it is impossible that two clients concurrently update a journal persisted in MongoDB. You can register the pessimistic locking listener to the synchronous service bus:

SimpleMongoListenerClient client = SimpleMongoListenerClient.create("mongodb://localhost:12345");
SimpleMongoUpdateListener updateListener = SimpleMongoUpdateListener.create(client.getMongoClient(), "testDb", "testCol", managedType, BarbelHistoContext.getDefaultGson());
SimpleMongoLazyLoadingListener loadingListener = SimpleMongoLazyLoadingListener.create(client.getMongoClient(), "testDb", "testCol", managedType, BarbelHistoContext.getDefaultGson());
MongoPessimisticLockingListener lockingListener = MongoPessimisticLockingListener.create(client.getMongoClient(), "lockDb", "docLocks");
BarbelHisto<DefaultPojo> mongoBackedHisto = BarbelHistoBuilder.barbel().withSynchronousEventListener(updateListener)
                            .withSynchronousEventListener(loadingListener).withSynchronousEventListener(lockingListener);

In this setup it's perfectly safe to access the version data from mutliple instances of BarbelHisto at the same time.