Let's write some history - DPC 2015

45 minute talk on Event Sourcing. Given on Dutch PHP Conference 2015

Transcript

1. 1/92 Event Sourcing Let's write some history https://joind.in/14226
2. Willem-Jan Zijderveld @willemjanz github.com/wjzijderveld  
3. Rotterdam http://labs.qandidate.com
4. Broadway Event Sourcing and CQRS library for PHP github.com/qandidate-labs/broadway
5. Event Sourcing
6. You are throwing away data!
7. Only most recent state gets stored
8. What was the previous state?
9. Why did the state change?
10. It's hard to keep track of all the data
11. A company has one or more connected accounts
12. A company has one or more enabled applications
13. An account has access to one or more applications
15. Complicated solutions to store and retrieve the data
16. But we manage Until...
17. Boss: Which accounts received access to application X in December?
18. "We'll add a timestamp and we will know" From that point in time
19. With CRUD you lose information You only store the last known information
20. Revoking access to an application for an account
21. You could lose when the access was revoked
22. You could lose why it got revoked
23. You could lose for which application it was revoked
24. You wouldn't know anything anymore
25. Let's assume you have a soft-delete in place
26. Boss: I want to know for which applications access got revoked more than once in the last year
27. 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 Past revocations are gone
28. How does Event Sourcing help me with that?
29. Store your data in a different way
30. Record what has changed The resulting state becomes a natural effect
31. EventStream
32. A serie of facts CompanyRegistered AppEnabled AccountConnected AccessGrantedToApp
33. Been there, done that
34. Single source of truth One source to rule all state The events cannot lie, it happened, deal with it
35. Your version control is event sourced
36. Sure thing, but how? There isn't one true answer
37. Event Sourcing DDD CQRS All 3 are optional, but work very nice together
38. Domain Driven Design The business should be reflected in your code
39. Entity An model with an identity
40. Aggregate root Responsible for keeping a group of entities consistent
41. I want to update my model How do I do that?
42. Record the change
43. 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 ; }
44. But we want to record an event
45. < ? 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 ; }
46. 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 ) ; } Just one possible implementation
47. / / 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 ( ) ; }
48. Save your events in an eventstore
49. Reloading your model
50. < 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 ; }
51. < ? 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 ) ; } }
52. Domain Message A message to tell your application what happened
53. DomainMessage Identifier Sequencenumber Payload Timestamp Metadata
54. Identifier + sequence number
55. Payload The event itself, it tells you what happened
56. 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 }
57. Timestamp It tells you when it happened
58. Metadata Descriptive, not structural
59. Let's look at some other events CompanyRegistered AppEnabled AccountConnected AccessGrantedToApp
60. 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 ( ) ; }
61. 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 ] = $ e v e n t - > g e t A c c o u n t I d ( ) ; }
62. 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 ; }
63. 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 ] = $ e v e n t - > g e t A c c o u n t I d ( ) ; }
64. We can retrieve all AccessGranted events for December
66. Won't this be slow?
67. CQRS Command Query Responsibility Segregation
68. Separate your writes and your reads
69. Read Models Create them from events using projections Specific read models for specific views in your application
70. 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 ) { / / . . } }
71. 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 ) ; } }
72. Use the right tool for the right job
73. Possibilities are endless
74. 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
75. So.. how does this flow work in an application? We'll use Commands
76. The write part of CQRS
77. Command & CommandHandler A CommandHandler deals with Commands and communicates with the Aggregate root
78. From Controller to CommandHandler 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 ' ) ) ) ; } }
79. 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 ) ; } }
80. 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 ( ) ; }
81. From Aggregate 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 ) ; }
82. 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 ) ; } }
83. Controller -> CommandBus -> CommandHandler -> AggregateRoot -> Event -> EventStore -> EventBus -> Projectors -> Read Model
84. Quite a bit to chew Try not to reinvent everything yourself
85. Testing Scenario based testing Given - When - Then
86. 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 ) ] ) ;
87. 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 ) ] ) ;
88. 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 ' ) ] ) ;
89. Time travel is possible! Use events you recorded to create a new report multiple years after the fact
90. You made a mistake in a projection? So what? Correct your projector and recreate your read model from your event stream
91. Questions? joind.in/14226 @willemjanz Freenode: #qandidate
92. 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/