Let's write some History - PHPBenelux 2016

In this talk I’m going to explain how Event Sourcing can help you solve this problem and what other benefits you can get from it.
We will walk over of the concepts and possible implementations of event sourcing.

1. 1/101 Event Sourcing Let's write some history https://joind.in/talk/6bf57
2. Willem-Jan Zijderveld @willemjanz github.com/wjzijderveld  
3. Rotterdam http://labs.qandidate.com
4. Broadway Event Sourcing/CQRS library for PHP github.com/qandidate-labs/broadway
5. Event Sourcing
6. You are throwing away data!
7. Only state gets stored
8. Only the most recent state gets stored
9. What was the previous state?
10. Why did the state change?
11. It's hard to keep track of all the data
12. An example
13. A company has one or more connected accounts
14. A company has one or more enabled applications
15. An account has access to one or more applications
17. Complicated solutions to store and retrieve the data
18. But we manage Until...
19. Boss: Which accounts received access to application X in December?
20. "We'll add a timestamp and we will know" From that point in time
21. With CRUD you lose information You only store the last known information
22. Another example
23. Revoking access to an application for an account Just remove the row in our join table
24. You could lose when the access was revoked
25. You could lose why it got revoked
26. You could lose for which application it was revoked
27. You wouldn't know anything anymore
28. Let's assume you have a soft-delete in place
29. Boss: I want to know for which applications access got revoked more than once in the last year
30. Keep track of revocations account_id app_id datetime 75623 8 2015-01-01T00:00:00+0000 75623 8 2015-01-27T18:54:18+0000 Are you going to do this for all actions on accounts?
31. How does Event Sourcing help me with that?
32. Store your data in a different way
33. Record what has happened The resulting state becomes a natural effect
34. EventStream
35. A serie of facts CompanyRegistered AppEnabled AccountConnected AccessGrantedToApp
36. Been there, done that
37. Single source of truth One source to rule all state The events cannot lie, it happened, deal with it
38. You have been working with this system
39. Your version control is event sourced
40. Sure thing, but how? "It depends"
41. Event Sourcing DDD CQRS All 3 are optional, but work very nice together
42. Domain Driven Design Let the events tell the story The business should be reflected in your code
43. Entity An model with an identity
44. Aggregate root Responsible for keeping a group of entities consistent
45. I want to create/update my model How do I do that?
46. Record what happened
47. You normally might do it like this < ? p h p / / C o m p a n y . p h p p u b l i c f u n c t i o n _ _ c o n s t r u c t ( $ i d , $ n a m e ) { $ t h i s - > i d = $ i d ; $ t h i s - > n a m e = $ n a m e ; }
48. But we want to record an event
49. < ? p h p / / C o m p a n y . p h p p u b l i c s t a t i c f u n c t i o n r e g i s t e r ( $ i d , $ n a m e ) { $ c o m p a n y = n e w C o m p a n y ( ) ; $ c o m p a n y - > a p p l y ( n e w C o m p a n y R e g i s t e r e d E v e n t ( $ i d , $ n a m e ) ) ; r e t u r n $ c o m p a n y ; }
50. Record the events < p h p / / A g g r e g a t e R o o t . p h p p u b l i c f u n c t i o n a p p l y ( $ e v e n t ) { $ t h i s - > h a n d l e ( $ e v e n t ) ; $ t h i s - > u n c o m m i t e d E v e n t s [ ] = $ e v e n t ; } p r i v a t e f u n c t i o n h a n d l e ( $ e v e n t ) { $ c l a s s P a r t s = e x p l o d e ( ' \ \ ' , $ e v e n t ) ; $ m e t h o d = ' a p p l y ' . e n d ( $ c l a s s P a r t s ) ; $ t h i s - > $ m e t h o d ( $ e v e n t ) ; }
51. / / C o m p a n y . p h p p u b l i c f u n c t i o n a p p l y C o m p a n y R e g i s t e r e d E v e n t ( C o m p a n y R e g i s t e r e d E v e n t $ e v e n t ) { $ t h i s - > c o m p a n y I d = $ e v e n t - > g e t C o m p a n y I d ( ) ; $ t h i s - > c o m p a n y N a m e = $ e v e n t - > g e t C o m p a n y N a m e ( ) ; }
52. Save your events in an eventstore
53. Current situation
54. Reloading your model
55. < p h p / / C o m p a n y R e p o s i t o r y . p h p f u n c t i o n l o a d ( $ a g g r e g a t e I d ) { $ e v e n t s = $ t h i s - > e v e n t S t o r e - > l o a d ( $ a g g r e g a t e I d ) ; $ a g g r e g a t e = n e w $ t h i s - > a g g r e g a t e C l a s s ( ) ; $ a g g r e g a t e - > i n i t i a l i z e S t a t e ( $ e v e n t s ) ; r e t u r n $ a g g r e g a t e ; }
56. < ? p h p / / C o m p a n y . p h p p u b l i c f u n c t i o n i n i t i a l i z e S t a t e ( a r r a y $ e v e n t s ) { f o r e a c h ( $ e v e n t s a s $ e v e n t ) { $ t h i s - > h a n d l e ( $ e v e n t ) ; } }
57. Domain Message A message to tell your application what happened
58. DomainMessage Identifier Sequencenumber Payload Timestamp Metadata
59. Identifier + sequence number
60. Payload The event itself, it tells you what happened
61. Should contain everything It should only depend on previous events f i n a l c l a s s C o m p a n y R e g i s t e r e d E v e n t { p r i v a t e $ c o m p a n y I d ; p r i v a t e $ c o m p a n y N a m e ; / / c o n s t r u c t o r + g e t t e r s }
62. Timestamp It tells you when it happened
63. Metadata Descriptive, not structural
64. Let's look at some other events CompanyRegistered AppEnabled AccountConnected AccessGrantedToApp
65. CompanyRegistered / / C o m p a n y f u n c t i o n a p p l y C o m p a n y R e g i s t e r e d E v e n t ( C o m p a n y R e g i s t e r e d E v e n t $ e v e n t ) { $ t h i s - > c o m p a n y I d = $ e v e n t - > g e t C o m p a n y I d ( ) ; }
66. AccountConnected / / C o m p a n y f u n c t i o n a p p l y A c c o u n t C o n n e c t e d E v e n t ( A c c o u n t C o n n e c t e d E v e n t $ e v e n t ) { $ i d = $ e v e n t - > g e t A c c o u n t I d ( ) ; $ t h i s - > a c c o u n t s [ $ i d ] = $ i d ; }
67. AppEnabled / / C o m p a n y f u n c t i o n a p p l y A p p E n a b l e d E v e n t ( A p p E n a b l e d E v e n t $ e v e n t ) { $ s u b s c r i p t i o n = n e w S u b s c r i p t i o n ( $ e v e n t - > g e t C o m p a n y I d ( ) , $ e v e n t - > g e t A p p I d ( ) ) ; $ t h i s - > s u b s c r i p t i o n s [ $ e v e n t - > g e t A p p I d ( ) ] = $ s u b s c r i p t i o n ; }
68. AccessGrantedToApp / / C o m p a n y p r o t e c t e d f u n c t i o n g e t C h i l d E n t i t i e s ( ) { r e t u r n $ t h i s - > s u b s c r i p t i o n s ; } / / S u b s c r i p t i o n f u n c t i o n a p p l y A c c e s s G r a n t e d T o A p p E v e n t ( A c c e s s G r a n t e d T o A p p E v e n t $ e v e n t ) { i f ( $ t h i s - > a p p I d ! = = $ e v e n t - > g e t A p p I d ( ) ) { r e t u r n ; } $ a c c o u n t I d = $ e v e n t - > g e t A c c o u n t I d ( ) ; $ t h i s - > g r a n t e d A c c o u n t s [ $ a c c o u n t I d ] = $ a c c o u n t I d ; }
69. We can retrieve all AccessGranted events for December
70. Won't this be slow?
71. CQRS Command Query Responsibility Segregation
72. Separate your writes and your reads
73. Read Models Create them from events using projections Specific read models for specific views in your application
74. EventBus All events go onto the event bus after being saved
75. CompanyRegistration c l a s s C o m p a n y R e g i s t r a t i o n i m p l e m e n t s R e a d M o d e l { p u b l i c f u n c t i o n _ _ c o n s t r u c t ( $ c o m p a n y I d , $ c o m p a n y N a m e , D a t e T i m e $ r e g i s t e r e d O n ) { / / . . } }
76. Company Registration Projector c l a s s C o m p a n y R e g i s t r a t i o n P r o j e c t o r i m p l e m e n t s E v e n t L i s t e n e r { p u b l i c f u n c t i o n a p p l y C o m p a n y R e g i s t e r e d E v e n t ( C o m p a n y R e g i s t e r e d E v e n t $ e v e n t , D o m a i n M e s s a g e $ d o m a i n M e s s a g e ) { $ c o m p a n y = n e w C o m p a n y R e g i s t r a t i o n ( $ e v e n t - > g e t C o m p a n y I d ( ) , $ e v e n t - > g e t C o m p a n y N a m e ( ) , $ d o m a i n M e s s a g e - > g e t R e c o r d e d O n ( ) ) ; $ t h i s - > r e p o s i t o r y - > s a v e ( $ c o m p a n y ) ; } }
77. Use the right tool for the right job
78. Possibilities are endless
79. The ability to create multiple read models List of company registrations Graph of all connections between companies and accounts Creating reports about the amount of revocations
80. So.. how does this flow work in an application?
82. The C in CQRS
83. The write part of CQRS
84. Command & CommandHandler A CommandHandler deals with Commands and communicates with the Aggregate root
85. From Controller to CommandBus c l a s s C o m p a n y C o n t r o l l e r { f u n c t i o n r e g i s t e r A c t i o n ( R e q u e s t $ r e q u e s t ) { $ t h i s - > c o m m a n d B u s - > d i s p a t c h ( n e w R e g i s t e r C o m p a n y C o m m a n d ( U u i d : : u u i d 4 ( ) , $ r e q u e s t - > r e q u e s t - > g e t ( ' c o m p a n y N a m e ' ) ) ) ; } }
86. From CommandHandler to Aggregate c l a s s C o m p a n y C o m m a n d H a n d l e r { f u n c t i o n h a n d l e R e g i s t e r C o m p a n y C o m m a n d ( R e g i s t e r C o m p a n y C o m m a n d $ c o m m a n d ) { $ c o m p a n y = C o m p a n y : : r e g i s t e r ( $ c o m m a n d - > g e t C o m p a n y I d ( ) , $ c o m m a n d - > g e t C o m p a n y N a m e ( ) ) ; $ t h i s - > a g g r e g a t e R e p o s t i t o r y - > s a v e ( $ c o m p a n y ) ; } }
87. From Aggregate to Event p u b l i c s t a t i c f u n c t i o n r e g i s t e r ( $ c o m p a n y I d , $ n a m e ) { $ c o m p a n y = n e w C o m p a n y ( ) ; $ c o m p a n y - > a p p l y ( n e w C o m p a n y R e g i s t e r e d E v e n t ( $ c o m p a n y I d , $ n a m e ) ) ; r e t u r n $ c o m p a n y ; } p u b l i c f u n c t i o n a p p l y C o m p a n y R e g i s t e r e d E v e n t ( C o m p a n y R e g i s t e r e d E v e n t $ e v e n t ) { $ t h i s - > c o m p a n y I d = $ e v e n t - > g e t C o m p a n y I d ( ) ; }
88. From Repository to EventStore / / C o m p a n y R e g i s t r y . p h p f u n c t i o n s a v e ( $ a g g r e g a t e ) { $ e v e n t s = $ a g g r e g a t e - > g e t U n c o m m i t t e d E v e n t s ( ) ; $ t h i s - > e v e n t S t o r e - > a p p e n d ( $ a g g r e g a t e - > g e t A g g r e g a t e I d ( ) , $ e v e n t s ) ; $ t h i s - > e v e n t B u s - > p u b l i s h ( $ e v e n t s ) ; }
89. From event to read model c l a s s C o m p a n y R e g i s t r a t i o n P r o j e c t o r { p u b l i c f u n c t i o n a p p l y C o m p a n y R e g i s t e r e d E v e n t ( C o m p a n y R e g i s t e r e d E v e n t $ e v e n t , D o m a i n M e s s a g e $ d o m a i n M e s s a g e ) { $ c o m p a n y = n e w C o m p a n y R e g i s t r a t i o n ( $ e v e n t - > g e t C o m p a n y I d ( ) , $ e v e n t - > g e t C o m p a n y N a m e ( ) , $ d o m a i n M e s s a g e - > g e t R e c o r d e d O n ( ) ) ; $ t h i s - > r e p o s i t o r y - > s a v e ( $ c o m p a n y ) ; } }
90. Quite a bit to chew
92. But we are not done yet!
93. Testing
94. Scenario based testing Given - When - Then
95. Test your Command Handler $ t h i s - > s c e n a r i o - > g i v e n ( [ n e w C o m p a n y R e g i s t e r e d E v e n t ( 1 2 3 ) ] ) - > w h e n ( n e w E n a b l e A p p F o r C o m p a n y C o m m a n d ( 4 2 , 1 2 3 ) ) - > t h e n ( [ n e w A p p E n a b l e d E v e n t ( 4 2 , 1 2 3 ) ] ) ;
96. Or your aggregate $ t h i s - > s c e n a r i o - > g i v e n ( [ n e w C o m p a n y R e g i s t e r e d E v e n t ( 1 2 3 ) ] ) - > w h e n ( f u n c t i o n ( $ c o m p a n y ) { $ c o m p a n y - > e n a b l e A p p ( 4 2 ) ; } ) - > t h e n ( [ n e w A p p E n a b l e d E v e n t ( 4 2 , 1 2 3 ) ] ) ;
97. Don't forget your read models $ t h i s - > s c e n a r i o - > g i v e n ( [ ] ) - > w h e n ( n e w C o m p a n y R e g i s t e r e d E v e n t ( 1 2 3 , ' A c m e I n c ' ) ) - > t h e n ( [ n e w C o m p a n y R e g i s t r a t i o n ( 1 2 3 , ' A c m e I n c ' ) ] ) ;
98. Time travel is possible! Use events you recorded to create a new report multiple years after the fact
99. You made a mistake in a projection? So what? Correct your projector and recreate your read model from your event stream
100. Questions? https://joind.in/talk/6bf57 @willemjanz Freenode: #qandidate
101. More information http://codebetter.com/gregyoung/2010/02/20/why-use- event-sourcing/ http://codebetter.com/gregyoung/2010/02/13/cqrs-and- event-sourcing/ http://martinfowler.com/eaaDev/EventSourcing.html http://martinfowler.com/bliki/CQRS.html http://www.axonframework.org/docs/2.3/domain- modeling.html http://labs.qandidate.com/