Slides from Code Mastery meetup 22 Mar 2017

1. CQRS EXPLAINED
DARIUSZ SADOWSKI (@DARSADOW)

2. AT THE BEGINNING
THERE WAS CRUD

3. STATE IS
EVERYTHING

4. COMMAND-QUERY
SEPARATION

5. COMMAND

6. QUERY

7. FIRST STEP INTO
BETTER WORLD

8. REAL WORLD

9. IN PRACTICE
▸Command as a Request
▸Command Handler
▸Response is optional
▸… but it can be very helpful
▸State is still your main concern

10. STATE CHANGE ONLY IN
COMMAND HANDLER

11. COMMAND REFLECTS ONE
INTERACTION WITH THE
SYSTEM

12. WHEN INTERACTION
CHANGES ONLY ONE
HANDLER NEEDS TO CHANGE

13. WHO CARES
ABOUT QUERIES?!

14. LETS ADD THE
MISSING “R”

15. SEPARATION ON
DEEPER LEVEL

16. WRITE MODEL

17. READ MODEL

18. BUT WHY?

19. WHY TO SEPARATE READ MODEL?
▸Prepare data for many different views
▸Transformation at write to keep data
readable
▸Integration with other systems
▸Performance

20. LETS TALK ABOUT
WHAT HAPPENED

21. EVENT IS A DESCRIPTION
OF THE FACT OF THE PAST

22. COMMAND IS A
COMMAND ;)

23. FROM COMMAND
TO THE EVENT

24. EVENT CAN BE ADDED
BUT CAN’T BE MODIFIED

25. MATERIALISED
VIEWS

26. WHEN YOU KNOW WHAT
HAPPENED YOU CAN DO
QUITE A LOT WITH IT

27. TEXT
{GOOD THINGS} ABOUT EVENT SOURCING
▸Replay-ability
▸Undo
▸Audit trail
▸Reactive system modelling

28. DOWNSIDES OF
CQRS/ES

29. SUMMARY

30. THANK YOU