Session & Transaction Support

Support two levels of transactions - transaction that wrap the SaveChanges call from the MongoDbContext and the internal batch write calls in the DbEntityWriter.

https://mongodb.github.io/mongo-csharp-driver/2.7/what_is_new/ https://mongodb.github.io/mongo-csharp-driver/2.7/reference/driver/crud/sessions_and_transactions/

Will need to maintain backwards compatibility when the MongoDB server isn’t running v4

More investigation will be required on how best to implement this functionality.

[dthk-cogmatix]

Thoughts from “the field.”

I’ve been running a my own patched version of MongoFramework for the past 9 months where I’ve added session/transaction support. I’ve been using a Mongo Client pre 4.4 and have approached indexes and collection creation as a manual activity prior to code deployment. This is similar to (older) Entity Framework behavior, unless you specify in initialization to have Entity Framework handle the schema creation. I don’t see a “huge” issue here, but it definitely doesn’t feel as clean, polished, or robust.

Thoughts on how to handle this: #1) Imitate Entity Framework behavior. Create initialization handlers/code that allow the developer to specify initialization behavior. Delete(), Create(), CreateIfNotExists(), EnsureCreated(), etc. It seems like the executing context of this code wouldn’t really require a session. This seems like the appropriate time to check if Collections exist for all entities and if any necessary indexes are in place.

#2) Further simplify the process and have an option flag that is like: AutoCreateCollections. Document behavior and call it good enough for now. If someone is using client 4.4+ and sets this to true, no issue. If it’s set to true and the client is 4.2, they will receive an exception during creation. Not terrible…

#3) Prioritize operations and executions: Pre-Transaction and during Transaction. If you’re tracking all changes locally before submitting to the server, you could then prioritize execution of collections/indexes before beginning a transaction and sending to the server.

I’m not sure how the code in the latest version is looking, but that may dictate which approach is most appropriate.

[dthk-cogmatix]

I like what you’ve proposed and it’s a much more thoughtful implementation of what I’ve mentioned above. I completely agree with wrapping the Session and usage of IDisposable. I think the only other add I would consider is putting an IsDisposed property on the Session? That way you can minimize having to catch and swallow ObjectDisposedExceptions?