There's a ton of theory available on DDD, event sourcing and CQRS but how does one get's started in terms of code? Moreover, when we have a tight deadline, one wants to solely focus on solving core business problems rather than getting caught up by plumbing non-functional concerns such as snapshotting, command handling, guaranteed events delivery to the right event listeners, events replaying, persisting aggregate, etc. In this talk, we will build an application to see how Axon Framework supports CQRS and Event sourcing by providing a robust implementation for fundamental building blocks such as event dispatching mechanism, aggregates, repositories, event sourcing, Domain Events, etc.to build scalable, extensible and maintainable applications. Furthermore, Axon provides extensive support for Spring which means much of the configuration can be avoided by leveraging Spring's annotation support.

1. CQRS & EventSourcing With Spring & Axon
By :
Nakul Mishra
“Success by design is infinitely better than a win by chance.”
#DevoxxPL @nklmish

2. #DevoxxPL @nklmish

3. Code is like water, it reflects
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4. Our perception
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5. Business Reality
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6. DDD
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7. #DevoxxPL @nklmish
DDD - Focus on domain

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DDD In Practice?

9. #DevoxxPL @nklmish
Place behaviour in “Domain Model”
DDD in a nutshell

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DDD in a nutshell
Code should reflect “Business REALITY”
(Ubiquitous language)
Place behaviour in “Domain Model”

11. #DevoxxPL @nklmish
Provide unit of consistency
across Domain Model via “Aggregate”
DDD in a nutshell
Code should reflect “Business REALITY”
(Ubiquitous language)
Place behaviour in “Domain Model”

12. #DevoxxPL @nklmish
Define clear “bounded context” &
protect your model.
DDD in a nutshell
Provide unit of consistency
across Domain Model via “Aggregate”
Code should reflect “Business REALITY”
(Ubiquitous language)
Place behaviour in “Domain Model”

13. Aggregate
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14. Event Sourcing
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15. Traditional app
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16. Traditional app - What Happened
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12345 1 Veggie Burger Shipped

17. Event sourcing
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18. Event Sourcing - What ACTUALLY
Happened
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Item Added 1 Veggie Burger

19. Event Sourcing - What ACTUALLY
Happened
#DevoxxPL @nklmish
Item Added 1 Veggie Burger
Item Added 1 Salad

20. Event Sourcing - What ACTUALLY
Happened
#DevoxxPL @nklmish
Item Added 1 Veggie Burger
Item Added 1 Salad
Item Added 1 Ice cream

21. Event Sourcing - What ACTUALLY
Happened
#DevoxxPL @nklmish
Item Added 1 Veggie Burger
Item Added 1 Salad
Item Added 1 Ice cream
Item Removed 1 Ice cream

22. Event Sourcing - What ACTUALLY
Happened
#DevoxxPL @nklmish
Item Added 1 Veggie Burger
Item Added 1 Salad
Item Added 1 Ice cream
Item Removed 1 Ice cream
Item Removed 1 Salad

23. Event Sourcing - What ACTUALLY
Happened
#DevoxxPL @nklmish
Item Added 1 Veggie Burger
Item Added 1 Salad
Item Added 1 Ice cream
Item Removed 1 Ice cream
Item Removed 1 Salad
OrderConfirmed

24. Event Sourcing - What ACTUALLY
Happened
#DevoxxPL @nklmish
Item Added 1 Veggie Burger
Item Added 1 Salad
Item Added 1 Ice cream
Item Removed 1 Ice cream
Item Removed 1 Salad
OrderConfirmed
Order Shipped

25. Event Sourcing - What ACTUALLY
Happened
#DevoxxPL @nklmish
Item Added 1 Veggie Burger
Item Added 1 Salad
Item Added 1 Ice cream
Item Removed 1 Ice cream
Item Removed 1 Salad
OrderConfirmed
Order Shipped
Food for Big Data, ML, etc.

26. Where to store events?
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27. Event Store
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28. Event Store
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Time

29. Event Store
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Time

30. Event Store
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Time

31. Event Store
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Time

32. Event Store
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Time

33. Event Store
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validate sequence number
Time

34. Event Store Implementation
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• EventStore - Greg Young
• AxonDB - AxonIQ
• Relational DBMS
• Roll out your own….

35. CQRS
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36. #DevoxxPL @nklmish
I WANT SOMETHING DONE
Command

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I WANT TO KNOW SOMETHING
Query (Projections)

38. CQRS
Command Query
UI
Command
Model
Projections
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39. Command Query
UI
Command
Model
Projections
Events
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CQRS

40. Command Query
UI
Command
Model
Projections
Events
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CQRS
Event
Store

41. Command Query
UI
Command
Model
Projections
Events
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CQRS
Event
Store

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43. Really

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AxonFramework

47. Axon History
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2009 20182010 2011 2012 2013 2014 2015 20172016
First code

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2009 20182010 2011 2012 2013 2014 2015 20172016
First code
1st Production user
Axon History

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2009 20182010 2011 2012 2013 2014 2015 20172016
First code
1st Production user
Axon 1.0
Axon History

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2009 20182010 2011 2012 2013 2014 2015 20172016
First code
1st Production user
Axon 1.0 Axon 2.0
Axon History

51. #DevoxxPL @nklmish
2009 20182010 2011 2012 2013 2014 2015 20172016
First code
1st Production user
Axon 1.0
Axon 3.0
(design phase)
Axon 2.0
Axon History

52. #DevoxxPL @nklmish
2009 20182010 2011 2012 2013 2014 2015 20172016
First code
1st Production user
Axon 1.0
Axon 3.0
(design phase)
Axon 3.0Axon 2.0
Axon History

53. #DevoxxPL @nklmish
2009 20182010 2011 2012 2013 2014 2015 20172016
First code
1st Production user
Axon 1.0
Axon 3.0
(design phase)
Axon 3.0 AxonDB/AxonHubAxon 2.0
Axon History

54. Axon, Location Transparency + Other Stuff
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55. Demo
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“I hear and I forget. I see and I remember. I do and I understand.”- Confucius
https://github.com/nklmish/axon-casino

56. Complex Transaction
Management ?
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57. ACID?
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58. BASE
Basic Availability, Soft state, Eventual consistency
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59. Saga
• Use to manage BASE transactions.
• React on event
• Coordinates activities between
• Bounded contexts
• Aggregates
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60. #DevoxxPL @nklmish

61. Demo at Scale
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62. #DevoxxPL @nklmish
How Can YOU Find…

63. Commands?
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64. Aggregates?
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65. Bounded Context?
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66. DomainEvent?
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67. Projections?
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68. Policy?
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69. Etc?
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70. #DevoxxPL @nklmish

71. EventStorming = bringing together
people with questions & answers
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72. EventStorming = Brainstorming
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73. Event Storming, 10000 foot overview
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75. EventStorming
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77. Replace
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81. #DevoxxPL @nklmish
invoked on
EXTERNAL
SYSTEM
invoked on
DOMAIN
EVENT
POLICY
generates
generates
invokes
invokestriggers
translated into
Final Result == Engineering Input
COMMAND
AGGREGATE
READ MODEL
(PROJECTIONS)
COMMAND

82. Summary
• Domain first, technology later.
• DDD != perfection.
• CQRS + Event sourcing =
• Axon, theory to practise
• Event Storming == collective learning
• Learning & connecting dots
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83. Thank You
Q&A
#DevoxxPL @nklmish
https://github.com/nklmish/axon-casino
http://tiny.cc/lsauuy
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