CQRS and Event Sourcing

CQRS and Event Sourcing are becoming buzzwords nowadays. This presentation tries to clarify both concepts and present a simple example application, written with those powerful architectures

Transcript

1. CQRS EVENT SOURCING
5. Christian Soronellas Web Enthusiast @theUniC theUniC
8. Exploration of concepts (CQRS and ES) Practical use case Conclusions
9. #phpbcn https://github.com/theUniC/blog-cqrs
10. ¿What is CQRS?
11. It’s an architectural pattern
12. Asking a question should not change the answer
13. Methods that return state information should not trigger side effects
14. <?php ! namespace An\Awesome\Namespace; ! class AnAmazingService { /** @var An\Awesome\Dependency */ private $aDependency; ! public function getDependency() { if (null === $this->aDependency) { $this->aDependency = new \An\Awesome\Dependency(); } ! return $this->aDependency; } ! public function anIncredibleAction() { $aDependency = $this->getDependency(); $aDependency->performSomethingNeeded(); // ... } }
15. <?php ! namespace An\Awesome\Namespace; ! class AnAmazingService { /** @var An\Awesome\Dependency */ private $aDependency; ! public function getDependency() { if (null === $this->aDependency) { $this->aDependency = new \An\Awesome\Dependency(); } ! return $this->aDependency; } ! public function anIncredibleAction() { $aDependency = $this->aDependency; $aDependency->performSomethingNeeded(); // ... } }
16. CQRS challenges the assumption that reading and writing are supposed to share the same abstractions
17. <?php ! namespace AcmeShop\Billing\DomainModel\Order; ! interface OrderRepository { /** return Order */ public function get(OrderId $anId); }
18. <?php ! namespace AcmeShop\Billing\DomainModel\Order; ! interface OrderRepository { /** @return Order */ public function get(OrderId $anId); ! /** @return Order[] */ public function getByUser(UserId $aUserId); }
19. <?php ! namespace AcmeShop\Billing\DomainModel\Order; ! interface OrderRepository { /** @return Order */ public function get(OrderId $anId); ! /** @return Order[] */ public function byUser(UserId $aUserId); ! /** @return OrderWithAge[] */ public function allGroupedByAge(); }
20. <?php ! namespace AcmeShop\Billing\DomainModel\Order; ! interface OrderRepository { /** @return Order */ public function get(OrderId $anId); ! /** @return Order[] */ public function byUser(UserId $aUserId); ! /** @return OrderWithAge[] */ public function allGroupedByAge(); ! /** @return OrderWithCarrier[] */ public function allGroupedByCarrier(); }
21. Command sends Command Handler is handled by Write Model uses Event Subscriber triggers writes reads from Read Model queries User Interface synchronizes with returns
22. Command sends Command Handler is handled by Write Model uses Event Subscriber triggers writes reads from Read Model queries Eventual Consistency™ User Interface synchronizes with returns
23. Write Model Event Event Event Event
24. Events are fundamental part in DDD
25. We can express the system state as a sequence ! of events that have occurred
27. POST COMMENT has many belongs to AUTHOR is written by an writes many
28. [ { "type":"PostWasCreated", "created_at": "2014-06-11 18:00:00", "data":"{'post_id': 1, 'title': '...', 'content': '...'}" } ]
29. [ { "type":"PostWasCreated", "created_at": "2014-06-11 18:00:15", "data": "{'post_id': 1, 'title': '...', 'content': '...'}" }, { "type": "PostWasPublished", "created_at": "2014-06-11 18:05:35", "data": "{'post_id': 1}" } ]
30. [ { "type":"PostWasCreated", "created_at": "2014-06-11 18:00:15", "data": "{'post_id': 1, 'title': '...', 'content': '...'}" }, { "type": "PostWasPublished", "created_at": "2014-06-11 18:05:35", "data": "{'post_id': 1}" }, { "type": "CommentWasCreated", "created_at": "2014-06-11 18:15:20", "data": "{'post_id': 1, 'comment_id': 1, 'comment': '...'}" } ]
31. Event Event Event Event Store™
32. PostWasCreated CommentWasAdded PostWasPublished Event Store™
33. Event Sourcing
34. Practical use case
35. Conclusions
36. CQRS and ES combined provide a simple solution for complex problems
37. CQRS allow reads and writes to scale independently
38. Event Sourcing allow to perform a more efficient and more exhaustive debugging
39. Event Sourcing grants not to be tightly coupled with any structure nor any implementation
40. They’re not the silver bullet Use it wisely
41. ¡Thanks!