re: Document-Level Optimistic Concurrency in MongoDB
I run into this blog post talking about how to handle optimistic concurrency in MongoDB and it brought to mind a very fundamental difference in the design philosophy between RavenDB and MongoDB.
If you’ll read the associated blog post, you’ll see guidance on how to build a simple optimistic concurrency using the MongoDB API. It looks like a relatively straightforward thing, but there is a lot of complexity going on here.
With RavenDB, we have decided that the responsibility of such tasks is on us, and not our users. Here is how you’ll write the same thing in RavenDB:
session.Advanced.OptimisticConcurrency = true;
And you are done. There are also options to set it globally (for all actions), for a particular session, as shown above or for a particular document or documents in a bigger transaction. About the only thing that we don’t handle is retries if the update failed, to allow you to re-run your business logic.
The reason I’m writing this is actually at the very end of the post:
This works just fine if I “remember” to include that
Whereclause correctly, but there’s a better way if we want a general solution. For that, I’d do pretty much what I would have in the Life Beyond Distributed Transactions series – introduce a Repository, Unit of Work, and Identity Map.
This is exactly right. It looks trivial to do something like that when you are looking into a trivial scenario, but put it in a real application and the complexity sprouts. For example, try doing the same thing with multiple documents that need to change together. You have to implement quite a lot of code to do so (identity map, unit of work, hopefully not a repository ).
With RavenDB, all of that is just there and available for you. No need to do anything, It Just Works.