Hello, we are using DB2 and are considering using document managment store. First we thought about MongoDB, but it lack of ability to participate in transactions was a deal breaker for us. It apears though that DB2 has adopted MongoDB engine to provide the same functionality through DB2 Json store, on top of this it give ability to participate in transactions together with other systems(this is what the website claims). And also it claims to support the same API as mongoDB. Which leads me to the question:

Is DB2 json storage compatible enough with MongoDB to be compatible with Hibernate OGM as well, or it is not compatible enough.

Also since transaction capabilities are realy important for us, will possible access to DB2 json store through Hibernate OGM be transactional?

Thanks

I don't know the DB2 JSON store so I cannot comment about how similar it looks to MongoDB. Worse case, you would write a variation of the logic with a new DatastoreProvider and GridDialect. This is not trivial but that's how we abstract different NoSQL engines from the engine of Hibernate OGM.

Hibernate OGM can work with transactional or non transactional datastores. For example Neo4J and Infinispan are transactional. MongoDD, CouchDB are not.

Thank you for the answer. Another question. You said that Infinispan is transactional, but what happens when the underlying cache store is Non Transactional like MongoDB for example. Lets say that we have a transaction which sends updates to Oracle and within the same transaction makes updates to Infinispan which are physicaly persisted in the cache store. Lets suppose that the transaction fail on because of Oracle constraint violation for example, we have already inserted a value in Infinispan which is synchroneusly propagated to the cache store --> MongoDB in this case / Non transactional. The data in Oracle is rollbacked, the In Memory data in infinispan will be rolledback as well, what happens to the MongoDB ?

I guess it is not rolled back? Which mean that it doesn't matter that Infinispan is transactional if the underlying storage is non transactional. Correct ?

When I mention Infinispan here, I mention it as the backend. That's an alternative to MongoDB: we support Infinispan, EhCache, MongoDB, CouchDB, Neo4J.
Back to Infinispan, it is an XAResource so if your Oracle transaction fails, all changes to Infinispan will be rollbacked.

For Mongo or other datastores that do not support transactions, we are working on a ErrorReport API that we hope will morph into a compensation API. You can look at the work in progress at https://github.com/hibernate/hibernate-ogm/pull/501