My first year with event-sourcing @DeventerPHP 2018-05-03

Over the last couple of years, I have heard of Event sourcing but did'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.

Transcript

1. My first year with event-sourcing 2018-05-03 DeventerPHP
2. Tim Huijzers @Dragem Developer @ drukwerkdeal.nl Deventer NL
3. BeerWarehouse
4. Why use Event Sourcing
5. CRUD
6. We will save a new entry in our system because we just bought it and will store it in the fridge for later.
7. If we change the location the system only knows about that location.
8. We drank it so it’s not in the system anymore
9. We want to keep a history of everything we drank.
10. I want to know when I drank this in my history.
11. But that’s only for new beers.
12. Events
13. Same Information as before + Explicit action about what happened
14. Make Small Events
15. Removed Location and changed name because in the real world you might not know this yet.
16. When returning home I put the beer in my fridge
17. I need room in my fridge so I take it out. Using the same Event
18. And at last a event about when I consumed it.
19. 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.
20. “Every software program relates to some activity or interest of its user.” Eric Evans, Domain-Driven Design: Tackling Complexity in the Heart of Software
21. DDD
22. Some Principles • Ubiquitous Language • Entities • Value Objects • Aggregates • Bounded Context • Domain Events
23. “To communicate effectively, the code must be based on the same language used to write the requirements - the same language that the developers speak with each other and with domain experts.” Eric Evans, Domain-Driven Design: Tackling Complexity in the Heart of Software
24. When To Use Event Sourcing
25. • 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
26. When NOT To Use Event Sourcing
27. • 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
28. CQRS
29. “Every method should either be a command that performs an action, or a query that returns data to the caller, but not both. In other words, Asking a question should not change the answer.” Bertrand Meyer, Object-oriented Software Construction
30. Command
32. Query
34. Event Sourcing in code
35. Prooph
36. http://getprooph.org/
37. Command
42. Command Handler
45. Aggregate
47. Event
54. Back to the Aggregate
57. Think About Side Effects
60. Structuring your application
62. Understanding the DB
64. How many beers do I have?
65. How many different styles do I have?
66. How many beers have I drank last 30 days?
67. Projection
68. 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.
71. Pitfalls
72. Refactoring is harder, think about your architecture
73. Versioning • Change an Event • Make a new Event • Make the Event right from the start
74. Something wrong with the event
75. 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
76. What Now?
77. http://getprooph.org/
79. Snapshots
80. You Do Not Need Snapshots From The start
81. Trigger on Event Count
82. Pure Event Sourcing Is Not A Holy Grail
83. Do Not Save Personal Data In Events
84. Make Projections For All You Lists
85. Try It In A Hackathon First
86. Most Of The Time Your DB Is Not Holy
87. But I want to start yesterday! https://github.com/prooph/proophessor-do-symfony http://getprooph.org/
88. 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
89. Thanks, Any Questions? Example code from talk on: https://github.com/webbaard/BeerWarehouse