My first year with event sourcing-nijmegen

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Over the last couple of years, I have heard of Event sourcing but didn't really know where to start until I did a tutorial at DPC '17. After having some basic information it was time to start a Hackathon and after that something production worthy. In this talk I will try to give the best information to get started and to know some of the problems you can face if you begin event-sourcing.

Software

My first year with event-sourcing
PHP Nijmegen. 2018-06-20

My first year with event-sourcing
NMGN.tech. 2018-06-20

Tim Huijzers
@Dragem
Developer @ drukwerkdeal.nl
Deventer NL

First Try
● Limited knowledge
● No experience
● No ES framework
● Doomed from the start

Second Try
● Limited knowledge
● Limited experience
● New Framework
● New DI manager
● New ES Framework
● Doomed To Fail

Third Try
● Some knowledge
● Some experience
● Known framework
● known database
● known ES framework
● Still doomed

We will save a new entry in our system because we just
bought it and will store it in the fridge for later.

If we change the location the system only knows about that
location.

We drank it so it’s not in the system anymore

We want to keep a history of everything we drank.

I want to know when I drank this in my history.

Same Information as before + Explicit action about what
happened

Removed Location and changed name because in the real
world you might not know this yet.

When returning home I put the beer in my fridge

I need room in my fridge so I take it out. Using the same
Event

And at last a event about when I consumed it.

Crud
● I know what beer I have.
● I know when it was consumed.
● I know where it is.
Event-Sourcing
● I know what beer I have.
● I know when it was consumed.
● I know where it is.
● I know where it was before.
● I know when it was moved.
● I know where it was at any point in
time
● I know how many times it was moved.
● I know when it was added to the
system.
● I know what else was moved in that
day.

“Every software program relates to some
activity or interest of its user.”
Eric Evans, Domain-Driven Design: Tackling Complexity in the Heart
of Software

● You need an audit log
● You like scalability
● You want to separate the read and write of an application
● You want to replay event on a dev machine to get an accurate
situation of what the state was at a point in time.
● You want reporting but don’t know what yet.
● You are done with mapping objects to tables

● You only need a simple CRUD system.
● You are processing a lot of personal data.
● You just want to query a lot of things on the DB
● You are starting on a big project for production

How many beers have I drank last 30 days?

A Projection allows you to loop through all event (past and present) and build your
own views.
● Read Model
○ Define the data you would like to use.
● Projection
○ Loops through the events and applies that data to your view
● Finder
○ Helps you find data from that view.

Refactoring is harder, think about your
architecture

Versioning
● Change an Event but support the old version
● Make a new Event
● Make the Event right from the start

Event are immutable, So don’t change them
● Try solving it another way first.
● Correct errors with new events
● Try a upcaster
● Make a new stream and fill it with mutated events (and test)
● Change the events in the database

But what if I have like 100 trillion gazillion
events?

You Do Not Need Snapshots From The start

Source
https://github.com/prooph/proophessor-do-symfony
http://getprooph.org/

Other Tools
● Broadway
○ No Upcaster,
○ No Snapshots,
○ No Replaying
● Axon
○ Upcasting by MessageFactory,
○ Snapshots by Trigger on event count,
○ Replaying by Example code for replay
● Akka
○ Upcasting by Event Adapter,
○ Snapshots decided by actor,
○ Replaying

Thanks, Any Questions?
Example code from talk on:
https://github.com/webbaard/BeerWarehouse

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My first year with event sourcing-nijmegen

1. My first year with event-sourcing PHP Nijmegen. 2018-06-20

2. My first year with event-sourcing NMGN.tech. 2018-06-20

3. Tim Huijzers @Dragem Developer @ drukwerkdeal.nl Deventer NL

4. First Try ● Limited knowledge ● No experience ● No ES framework ● Doomed from the start

5. Second Try ● Limited knowledge ● Limited experience ● New Framework ● New DI manager ● New ES Framework ● Doomed To Fail

6. Third Try ● Some knowledge ● Some experience ● Known framework ● known database ● known ES framework ● Still doomed

9. BeerWarehouse

10. Why use Event Sourcing

11. CRUD

12. We will save a new entry in our system because we just bought it and will store it in the fridge for later.

13. If we change the location the system only knows about that location.

14. We drank it so it’s not in the system anymore

15. We want to keep a history of everything we drank.

16. I want to know when I drank this in my history.

17. But that’s only for new beers.

18.

19. Events

20. Same Information as before + Explicit action about what happened

21. Make Small Events

22. Removed Location and changed name because in the real world you might not know this yet.

23. When returning home I put the beer in my fridge

24. I need room in my fridge so I take it out. Using the same Event

25. And at last a event about when I consumed it.

26.

27. Crud ● I know what beer I have. ● I know when it was consumed. ● I know where it is. Event-Sourcing ● I know what beer I have. ● I know when it was consumed. ● I know where it is. ● I know where it was before. ● I know when it was moved. ● I know where it was at any point in time ● I know how many times it was moved. ● I know when it was added to the system. ● I know what else was moved in that day.

28. “Every software program relates to some activity or interest of its user.” Eric Evans, Domain-Driven Design: Tackling Complexity in the Heart of Software

29.

30. When To Use Event Sourcing

31. ● You need an audit log ● You like scalability ● You want to separate the read and write of an application ● You want to replay event on a dev machine to get an accurate situation of what the state was at a point in time. ● You want reporting but don’t know what yet. ● You are done with mapping objects to tables

32. When NOT To Use Event Sourcing

33. ● You only need a simple CRUD system. ● You are processing a lot of personal data. ● You just want to query a lot of things on the DB ● You are starting on a big project for production

34. Event Sourcing in code

35. Prooph

36. http://getprooph.org/

37.

38. Command

39.

40.

41.

42.

43. Command Handler

44.

45.

46. Aggregate

47.

48. Event

49.

50.

51.

52.

53.

54.

55. Back to the Aggregate

56.

57.

58.

59.

60. Think About Side Effects

61.

62.

63. Structuring your application

64.

65. Understanding the DB

66.

67. How many beers do I have?

68. How many different styles do I have?

69. How many beers have I drank last 30 days?

70. Projection

71. A Projection allows you to loop through all event (past and present) and build your own views. ● Read Model ○ Define the data you would like to use. ● Projection ○ Loops through the events and applies that data to your view ● Finder ○ Helps you find data from that view.

72.

73.

74. Pitfalls

75. Refactoring is harder, think about your architecture

76.

77. Versioning ● Change an Event but support the old version ● Make a new Event ● Make the Event right from the start

78. Something wrong with the event

79. Event are immutable, So don’t change them ● Try solving it another way first. ● Correct errors with new events ● Try a upcaster ● Make a new stream and fill it with mutated events (and test) ● Change the events in the database

80. But what if I have like 100 trillion gazillion events?

81.

82. Snapshots

83. You Do Not Need Snapshots From The start

84. Trigger on Event Count

85. Pure Event Sourcing Is Not A Holy Grail

86. Do Not Save Personal Data In Events

87. Make Projections For All You Lists

88. Try It In A Hackathon First

89. Most Of The Time Your DB Is Not Holy

90. What Now?

91. http://getprooph.org/

92.

93. Source https://github.com/prooph/proophessor-do-symfony http://getprooph.org/

94. Other Tools ● Broadway ○ No Upcaster, ○ No Snapshots, ○ No Replaying ● Axon ○ Upcasting by MessageFactory, ○ Snapshots by Trigger on event count, ○ Replaying by Example code for replay ● Akka ○ Upcasting by Event Adapter, ○ Snapshots decided by actor, ○ Replaying

95.

96. Thanks, Any Questions? Example code from talk on: https://github.com/webbaard/BeerWarehouse

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