Gentle introduction to CQRS

what if I say "CQRS + ES"? ... if you're already looking on wikipedia this talk is for you. CQRS and Event Sourcing introduction for acronyms haters. 100% fluff free

Transcript

1. …WHAT’S THAT CQRS THING? introduction for adopters effect free!
2. COMMAND QUERY RESPONSIBILITY SEGREGATION PATTERN
3. ORIGINAL SIN CREATE READ UPDATE DELETE
6. is an architectural pattern proposed by Greg Young that segregates reads and writes of a system into two separate subsystems. CQRS
7. writes are usually asynchronous and stored in a transactional storage while reads are eventually consistent and retrieved from de-normalised views CQRS (details)
8. BERTRAND MAYER Designer of Eiffel programming language Coined “open/closed principle” and “design by contract” Introduced command query separation (CQS)
9. Use of commands and queries separates write and read concerns
10. COMMAND Tell to do something
11. COMMAND • Command is the message to change state • Message handled by a CommandHandler • Returns void (so nothing) • Describes business intent • Immutable
12. QUERY Fetch state from data store
13. QUERY • Read state from data store • Does not change state • Has a return value
14. WHY SHOULD I USE CQRS? • Scalability • Reduced complexity • Flexibility • Focus on the business
15. • Fear of change • Mental leap • All-Or-Nothing approach BE AWARE OF
16. CQRS MYTHS • is easy • CQRS = Event Sourcing and vice versa • requires an eventual consistent read store • requires a bus/queues/asynchronous messaging
17. – Udi Dahan “Most people using CQRS (and event sourcing too) shouldn't have done so” – Greg Young “It's important to note though, that these are things you can do, not necessarily things you should do. Separating the read and write models can be quite costly” WHEN SHOULD I AVOID IT?
18. WHATS NEXT? • Event sourcing (ES) • Eventual consistency • Task based UI • …
20. Thank you. @realfuzzy Michele Franzin
21. CREDITS slide10 - www.defenceimagery.mod.uk - 45155579 slide 12 - https://www.flickr.com/photos/broeckxsven/ slides 4,9 - http://martinfowler.com/bliki/ http://martinfowler.com/bliki/CQRS.html http://udidahan.com/2009/12/09/clarified-cqrs/ https://en.wikipedia.org/wiki/Command–query_separation https://cqrs.files.wordpress.com/2010/11/cqrs_documents.pdf RESOURCES