CQRS: Storing events and publishing them - how do I do this in a safe way?

Question

As I\'ve learned in Why is the CQRS repository publishing events, not the event store? it\'s the CQRS repository\'s task to publish events. So far, so good.

Of cours

Answer 1

Your repository could publish events, it doesn't have to. The solution in this case is to use the event store as a queue. You would have a background process that monitors the event store for new events, publishes them to (for instance) a bus, and then marks them as dispatched.

As always, there are trade-offs. You'll likely have to deal with at-least-once messaging and idempotent processing. It's more complex than using a simple distributed transaction.

Jonathan Oliver has written several posts about this topic that might help you out: Removing 2PC, How I Avoid Two-Phase Commit, Idempotency Patterns