Rethink your architecture with CQRS

1. Rethinkyourarchitecturewith CQRS Pieter Joost van de Sande Passionated software developer, Atos Email: pj@born2code.net @twitter: pjvds

2. This is meant to be a take away!

3. Architecture

4. Architecture Presentation Domain Data

5. Presentation Why do we love it? Domain Data

6. model Domain Driven Design Eric Evans - 2003

7. The value of a structured Model

8. Who believes in this?

9. Structured models are always created from a single viewpoint!

15. A model can only be optimized for one thing… and one thing only!

16. Request data Update screen Send update Presentation layer Request DTO Send DTO Map DTO Map DTO Domain layer RequestDTO RequestDTO Send DTO Send DTO Map DTO Map DTO Map DTO Map DTO Data layer Query data Query data Query data Query data Write data Write data Write data Write data

17. TWO fundamentals

18. Information

19. Transitions

20. WRITING != READING

21. From 3-tier to CQRS Presentation layer Domain layer Data layer

22. Just re-order the tiers Presentation layer Data layer Domain layer

23. Switch dependency Presentation layer Data layer Domain layer

24. CQRS! Presentation layer Command side Query side Data layer Domain layer

25. Here we go! From concept toArchitecturE

26. User interface

27. Demand for information

28. Read side User interface

29. We read a lot

30. We have multiple screens to fill

31. Data should be close to us

32. Relational databases are sub optimal for view data!

33. SELECT CCUS.CUST_FIRST_NAME , CCUS.CUST_LAST_NAME , CINT.CUST_INTEREST_RANK , CILO.CUST_INTERST FROM CUST_CUSTOMER AS CCUS , CUST_INTEREST_LOOKUP AS CILO , CUST_INTEREST AS CINT WHERE ( CCUS.CUST_CITY = 'Singapore' AND CCUS.CUST_PROV_STATE = 'Singapore' AND CCUS.CUST_CODE IN ( SELECT COHE.CUST_CODE FROM CUST_ORDER_HEADER AS COHE , CUST_ORDER_STATUS AS COST WHERE ( COHE.CUST_ORDER_DATE >='2009-01-01 00:00:00.001' AND COST.CUST_ORDER_STATUS IN( 'Shipped', 'Back-ordered', 'In-process' ) AND COHE.CUST_ORDER_STATUS_CODE = COST.CUST_ORDER_STATUS_CODE ) ) AND CCUS.CUST_CODE = CINT.CUST_CODE AND CINT.CUST_INTEREST_CODE = CILO.CUST_INTEREST_CODE ) ORDER BY CCUS.CUST_LAST_NAME ASC , CCUS.CUST_FIRST_NAME ASC , CINT.CUST_INTEREST_RANK ASC Evil execution plan!

34. Getting data should be simple select * from x where y Examples: Get all products of user X Get total price of all orders of month May Bottom line

35. Read side User interface

36. Read side Read databases User interface

37. Read side Read databases Facade User interface

38. Read side Read databases Facade DTO’s User interface

39. Demand for change

40. I want to tell the system something

41. Read side Write side Read databases Facade DTO’s User interface

42. Read side Write side Read databases Facade Commandhandlers commands DTO’s User interface

43. Commands • Simple messagecontainsall info needed • Lowercoupling (law of demeter) • Causesa state transition • Contains the intend of the user • Exists in a bounded context • Examples: • AddProductToShoppingCart • PurchaseOrder • MoveUserToNewAddress • CorrectAddressForUser • FinalizeOrder

44. Commands example

45. Users don’t make changes for nothing, intent is important!

46. Users don’t make changes for nothing This intent has value! Change has intent Correct the address for user X Customer X moved to new address VS.

47. Read side Write side Read databases Facade Commandhandlers commands DTO’s User interface

48. Read side Write side Read databases Repository Facade Domein Commandhandlers commands DTO’s User interface

49. Event Sourcing

50. Events • Simple message that describes an event • Contains intent • Contains all the data related to the event • Past tense CustomerMoved { CustomerId, NewAddress }