An exploration of Event Sourcing and Command Query Responsibility Segregation

1. Event Sourcing
THE BEST UBIQUITOUS
PATTERN YOU’VE NEVER
HEARD OF
@blimpyacht

3. User: A
Balance: 427
User: B
Balance: 550

4. User: A
Balance: 427
User: B
Balance: 550

5. User: A
Balance: 427
User: B
Balance: 550
+5-5

6. Event Sourcing

7. Event Sourcing
http://www.avanscoperta.it/en/training/cqrs-event-sourcing-and-applying-domain-driven-design/

8. https://media.licdn.com/media/p/5/005/09f/2d8/3c9f5a5.jpg
Event Sourcing

9. Event Sourcing
Command Query Responsibility Segregation
(CQRS)

10. +4
-2
+5
+7
-4
+9
-3
-6
+2
+1
+1
-5 t(12) = 9
Event Sourcing

11. +4
-2
+5
+7
-4
+9
-3
-6
+2
+1
+1
-5
t(5) = 10
Event Sourcing

12. +4
-2
+5
+7
-4
+9
-3
-6
+2
+1
+1
-5
t(9) = 12
Event Sourcing

13. +4
-2
+5
+7
-4
+9
-3
-6
+2
+1
+1
-5
Event Sourcing
f ’(x) = A

14. +4
-2
+5
+7
-4
+9
-3
-6
+2
+1
+1
-5
Event Sourcing
+5
-4
+5

15. Res Gestae Divi Augusti

19. Primary

20. Primary

21. Primary

22. +4
-2
+5
+7
-4
+9
-3
-6
+2
+1
+1
-5
Event Sourcing

23. +4
-2
+5
+7
-4
+9
-3
-6
+2
+1
+1
-5
t(4) = 14
Event Sourcing
t(8) = 10
t(12) = 9

25. Journal

26. Journal
Ledger

27. Accounts Payable
Journal
Ledger

28. Accounts Payable Accounts Receivab
Journal
Ledger

29. Command Query
Responsibility
Segregation

30. CQR
S

31. CRUD vs. CQRS
CRUD

32. CRUD vs. CQRS
WRIT
E
READ

33. WRIT
E
READ
Primar
y
READ
CRUD vs. CQRS

34. WRIT
E
Primar
y
READ
Variant Read Models: VIEWS
READ
READ
READ
READ

35. WRIT
E
READ
Primar
y
READ
CRUD vs. CQRS

36. CRUD vs. CQRS
2ndary
WRIT
E
READ
2ndary
Primar
y
READ

37. CRUD vs. CQRS
2ndary
WRIT
E
READ
2ndary
Primar
y
READ

38. Where it Gets Tricky

39. CRUD vs. CQRS
2ndary
WRIT
E
READ
2ndary
Primar
y
READ

40. CRUD vs. CQRS
2ndary
2ndary
Primar
y
WRIT
E
READ
READ

41. Consistent Replay
+4
-2
+5
+7
-4
+9
-3
-6
+2
+1
+1
-5
t(5) = 10 Exchange Rate
Server
10 / 0.88 = 8.82€

42. Consistent Replay
+4
-2
+5
+7
-4
+9
-3
-6
+2
+1
+1
-5
t(5) = 10 Exchange Rate
Server
10 / 0.87 = 8.70€

43. +4
-2
+5
+7
-4
+9
-3
-6
+2
+1
+1
-5
0.88
Exchange Rate
Server
Consistent Replay

44. Bounded Context
applicability of the model
internally consistent UNIFICATION

45. Where it Gets More Tricky

46. External Updates
+4
-2
+5
+7
-4
+9
-3
-6
+2
+1
+1
-5
Notification
Subscriber

48. http://www.webstaurantstore.com/images/products/extra_large/68

49. External Updates
+4
-2
+5
+7
-4
+9
-3
-6
+2
+1
+1
-5
Notification
SubscriberKafka

50. THANKS!
{ Name: ‘Bryan Reinero’,
Title: ‘Developer Advocate’,
Twitter: ‘@blimpyacht’,
Email: ‘bryan@mongdb.com’ }

51. {
"_id" : ObjectId("565f1dd8d4c6d9a90a9a16ce"),
"country" : "USA",
"crew" : "Ed White",
"vehicle" : "Gemini IV",
"date" : "6/3/65",
"duration" : "0:36",
"purpose" : "First U.S. EVA. Used HHMU and took photos,
"minutes" : 36
}
{
"_id" : ObjectId("565f1dd8d4c6d9a90a9a16cf"),
"country" : "USA",
"crew" : "Eugene Cernan",
"vehicle" : "Gemini IX-A",
"date" : "6/5/66",
"duration" : "2:07",
"purpose" : "Inadequate restraints stiff 25ft umbilical and high workloads….,
"minutes" : 127
}
{
"_id" : ObjectId("565f1dd8d4c6d9a90a9a16d0"),
"country" : "USA",
"crew" : "Mike Collins",
"vehicle" : "Gemini X",
"date" : "7/19/66",
"duration" : "0:50",

52. db.EVA.aggregate(
[
{ "$match": { "crew" : /David Scott/ } },
{ "$project": {
_id: 0,
name: { $literal: "David Scott" },
minutes: 1, }
},
{ "$group": { _id: "$name", total: { $sum: "$minutes" } } }
]
);
{ "_id" : "David Scott", "total" : 1200 }