This document discusses practical software architecture approaches including domain-driven design (DDD), command query responsibility segregation (CQRS), and event sourcing. It covers topics such as building a domain model, identifying aggregates, applying CQRS and event sourcing patterns, and using event-driven architectures with choreography and orchestration for managing systems. The overall aim is to provide guidance on implementing these architectural approaches beyond just buzzwords.

1. PRACTICAL SOFTWARE ARCHITECTURE
DDD, CQRS, EVENT SOURCING
@gboissinot
Grégory BOISSINOT
2021-03-04
Beyond buzzwords ?

2. 2
GRÉGORY BOISSINOT

3. STARTING
3

4. 4
OBJECTIVE : BUILDING A USEFUL DOMAIN MODEL #1
@gboissinot

5. 5
OBJECTIVE : BUILDING A USEFUL DOMAIN MODEL #2
@gboissinot

6. 6
OBJECTIVE : BUILDING A USEFUL DOMAIN MODEL #3
@gboissinot

7. 7
OBJECTIVE : BUILDING A USEFUL DOMAIN MODEL #4
@gboissinot

8. 8
OBJECTIVE : BUILDING A USEFUL DOMAIN MODEL #5
@gboissinot

9. 9
OBJECTIVE : BUILDING A USEFUL DOMAIN MODEL #6
@gboissinot

10. USE CASES
10
Business intents

11. 11
LISTING USE CASES
@gboissinot
Storytelling

12. 12
LISTING USE CASES
@gboissinot

13. 13
APPLYING DDD TACTICAL DESIGN PATTERNS
@gboissinot
Objects with rich behavior

14. 14
IDENTIFY AGGREGATES
@gboissinot
Driven by use cases
Respect for invariants
Aggregate as a
consistent unit

15. 15
AGGREGATES COMMUNICATION
@gboissinot
Driven by use cases
Aggregate as a
consistent unit

16. 16
APPLYING CLEAN ARCHITECTURE
@gboissinot
Get rid of Transaction Script

17. 17
USE CASE
@gboissinot

18. CQS
Command Query Separation
18

19. 19
COMMAND VS QUERY
@gboissinot

20. 20
COMMAND VS QUERY
@gboissinot
Commands & queries are simple POJOs
MARKED INTERFACE
MARKED INTERFACE

21. 21
COMMAND VS QUERY
@gboissinot

22. 22
COMMAND VS QUERY
@gboissinot

23. 23
COMMAND VS QUERY
@gboissinot
THE ASSOCIATED COMMAND
THE AGGREGATE ROOT
THE REPOSITORY

24. 24
COMMAND VS QUERY
@gboissinot
THE ASSOCIATED QUERY
THE REPOSITORY
QUERY HANDLER METHOD

25. 25
USING A SHARED REPOSITORY
@gboissinot

26. 26
SHARED REPOSITORY
@gboissinot

27. 27
COMMAND BUS & QUERY BUS
@gboissinot

28. 28
COMMAND BUS & QUERY BUS
@gboissinot

29. 29
COMMAND BUS & REST CONTROLER
@gboissinot

30. CQRS
30
Command Query Responsibility Segregation

31. 31
CQRS
@gboissinot
Reduce complexity with different models

32. 32
CQRS
@gboissinot
Single source
of truth
Replication

33. EVENT-DRIVEN
SYSTEMS
Event as the building block
33

34. 34
MODELLING WITH EVENTS
@gboissinot

35. 35
EVENT IDENTIFICATION PROCESS
@gboissinot

36. 36
DOMAIN EVENT
@gboissinot

37. 37
EVENT
@gboissinot
A SMIPLE DTO
ALL INFORMATION

38. 38
EVENT
@gboissinot

39. 39
EVENT DISPATCHER / EVENT HANDLER
@gboissinot

40. 40
COMMUNICATION WITH APPLICATION EVENTS
@gboissinot

41. 41
EVENT SOURCING
Events as the source of truth

42. 42
EVENT STORE
@gboissinot
Events as the source of truth
History of events.
The state by a replay of events.

43. 43
EVENT STREAMING
@gboissinot

44. 44
EVENT SOURCING
@gboissinot
Replaying all events to get the final state

45. 45
MODEL EVENT-DRIVEN
@gboissinot
Aggregates apply events

46. 46
EVENT STORE - EVENT SOURCING
@gboissinot
Single source
of truth

47. 47
CQRS & EVENT SOURCING
@gboissinot
Single source
of truth

48. 48
CQRS
@gboissinot

49. 49
MANAGING SYSTEMS
Choreography & Orchestration

50. 50
CHOREOGRAPHY
@gboissinot
No central coordinator. Simply know how to respond to events.
The participants are loosely coupled and don't have direct knowledge of each other.

51. 51
CHOREOGRAPHY
@gboissinot

52. 52
ORCHESTRATION
@gboissinot

53. 53
ORCHESTRATION - PROCESS MANAGER
@gboissinot
Knows the entire composition
Coordinates all parties
1

54. 54
ORCHESTRATION - PROCESS MANAGER
@gboissinot
2