CQRS and service bus

Question

CQRS is about separating commands and queries. We can add it easily using several patterns & technologies like Event Sourcing, DDD, NoSQL, etc... but is ServiceBus mandatory?

Answer 1

I'd say messaging and a service bus is optional.

CQRS simply means decomposing your application so that the Read and Write parts of your application can be optimized for the respective concern. Commands can be handled directy, even Events, if you decide to use them, can be dispatched synchronously.

A good reference for using an internal dispatcher is Greg Young's simple examle.

Update: Rob Ashton has just posted a very good article on what CQRS is and how not to make it more complicated than it actually is.

Answer 2

No serviceBus is not mandatory, it's simply one of the technologies that be used to implement CQRS, for example Event Pub/Sub. If anything, Event Sourcing & DDD have a closer relationship to CQRS than ServiceBus.