Repository and Unit of Work patterns - How to save changes

Question

I\'m struggling to understand the relationship between the Repository and Unit of Work patterns despite this kind of question being asked so many times. Essentially I still don\

Answer 1

Ehe, things are tricky. Imagine this scenario: one repo saves something in a db, other on the file system and the third something on the cloud. How do you commit that?

As a guideline, the UoW should commit things, however in the above scenario, Commit is just an illusion as you have 3 very different things to update. Enter eventual consistency, which means that all things will be consistent eventually (not in the same moment as you're used with a RDBMS).

That UoW is called a Saga in a message driven architecture. The point is every saga bit can be executed at different time. Saga completes only when all 3 repositories are updated.

You don't see this approach as often, because most of the time you'll work with a RDBMS, but nowadays NoSql is quite common so a classic transactional approach is very limited.

So, if you're sure you work ONLY with ONE rdbms, use a transaction with the UoW and pass teh associated connection to each repository. At the end, UoW will call commit.

If you know or expect you might have to work with more than one rdbms or a storage that doesn't support transactions, try to familiarize yourself with a message driven architecture and with the saga concept.