In this session, Stefan Alaerts will run you through the basics of CQRS.

1. CQ(R)S
Command-Query Responsibility Segregation

2. The typical CRUD architecture
http://en.wikipedia.org/wiki/Multitier_architecture

3. Command and Query Soup
• MVC application: POST includes a command (intent to act) and
returns a view based on a query.
• That doesn’t mean commands can’t have replies.
Replies are in the form of “sure, I’ll do that” or “no problem, done”

4. Command Query Separation (CQS)
• Queries: Return a result and do not change the observable state of
the system (are free of side effects).
• Commands: Change the state of a system but do not return a value.
Bertrand Meyer

8. More buzz words
• Domain Driven Design
• Event/Message Based design
• Distributed Applications
• EventSourcing
• Test Driven Development

9. Different kinds of ‘RS’
• EventSourcing + Reporting DB
• Different ViewModels for read and create/update (client level)
• Different databases or tables/views for read or write (DB level)
• …

10. The hexagonal architecture
http://alistair.cockburn.us/Hexagonal+architecture

11. Uncle Bob’s “Clean Architecture”
http://blog.8thlight.com/uncle-bob/2012/08/13/the-clean-architecture.html

12. Examples & Sources
• CQRS Journey
http://msdn.microsoft.com/en-us/library/jj554200.aspx
• CQRS, the book (Mark Nijhof)
https://github.com/MarkNijhof/Fohjin
• Lokad-CQRS
https://github.com/lokad/lokad-cqrs/
• CQRS (Martin Fowler)
http://martinfowler.com/bliki/CQRS.html
• Clarified CQRS (Udi Dahan)
http://www.udidahan.com/2009/12/09/clarified-cqrs/

13. Java Options
• Qi4j (framework for domain-centric application development)
http://qi4j.org/
• Axon Framework (cqrs framework)
http://www.axonframework.org/
• ServiceMix
http://servicemix.apache.org/
• Don’t forget the roll-your-own-KISS-YAGNI solution!

14. Demo Technology Stack
• Topshelf
• NServiceBus
• NancyFx
• OWIN