All aboard the Service Bus @ ZGPHP

We deal with complicated and complex applications on a daily basis, codebases that are filled with classes that do too many things. One design pattern that can help us with this is CQRS, Command Query Responsibility Seggregation. The idea behind CQRS is to split our models in two - the Command for writing, and the Query for reading. Applying CQRS can lead us to a more maintainable code, code that follows the SOLID principles more closely.

At the heart of CQRS lies the Service Bus - a transport mechanism responsible for dispatching our command, event, and query messages to their destinations.

This talk will give an overview of the CQRS pattern and take a closer look at the different types of service buses - command, event, and query ones. Main takeaway will be practical information on why, when, and how to use them, with emphasis on their differences. We'll also take a look at some of the PHP libraries out there that help us work with service buses like Prooph Service Bus, Simple Bus, Tactician, to name a few.

Transcript

1. Robert Bašić https://robertbasic.com/ @robertbasic All aboard the Service Bus
2. Robert Bašić ~ ZGPHP #78 A new project appears
3. Robert Bašić ~ ZGPHP #78 Ready to build greatness
4. Robert Bašić ~ ZGPHP #78 Your creation
5. Robert Bašić ~ ZGPHP #78 // todo finish this
6. Robert Bašić ~ ZGPHP #78 // refactor me later
7. Robert Bašić ~ ZGPHP #78 // dirty hack to work around...
8. Robert Bašić ~ ZGPHP #78 Same old story
9. Robert Bašić ~ ZGPHP #78 Same old story • An image gallery
10. Robert Bašić ~ ZGPHP #78 Same old story • An image gallery • Multiple currencies
11. Robert Bašić ~ ZGPHP #78 Same old story • An image gallery • Multiple currencies • Coupons
12. Robert Bašić ~ ZGPHP #78 Same old story • An image gallery • Multiple currencies • Coupons • Sales
13. Robert Bašić ~ ZGPHP #78 Same old story • An image gallery • Multiple currencies • Coupons • Sales • Reviews
14. Robert Bašić ~ ZGPHP #78 Same old story • An image gallery • Multiple currencies • Coupons • Sales • Reviews • With images
15. Robert Bašić ~ ZGPHP #78 Same old story • An image gallery • Multiple currencies • Coupons • Sales • Reviews • With images • Old products
16. Robert Bašić ~ ZGPHP #78 Same old story • An image gallery • Multiple currencies • Coupons • Sales • Reviews • With images • Old products • Warehousing
17. Robert Bašić ~ ZGPHP #78 Been there, done that
18. Robert Bašić ~ ZGPHP #78 Command Query Responsibility Segregation
19. Robert Bašić ~ ZGPHP #78 CQRS
20. Robert Bašić ~ ZGPHP #78 CQRS
21. Robert Bašić ~ ZGPHP #78 CQRS • Use cases
22. Robert Bašić ~ ZGPHP #78 CQRS • Use cases • Separation of concerns
23. Robert Bašić ~ ZGPHP #78 CQRS • Use cases • Separation of concerns • Improved readability
24. Robert Bašić ~ ZGPHP #78 CQRS • Use cases • Separation of concerns • Improved readability • Improved performance
25. Robert Bašić ~ ZGPHP #78 Before CQRS <?php namespace App\Service; class Product { public function update(array $product) { $presaveProduct = $this→getProductById($product['id']); if ($presaveProduct['sale'] == 1 && $presaveProduct['price'] != $product['price']) { throw new \Exception("Can't update price of products!"); } return $this->db->update('products', $product, ['id' => $product['id']]); } public function getProductById($productId) { /* ... */ } }
26. Robert Bašić ~ ZGPHP #78 After CQRS (i) <?php namespace App\Product\Command; use App\Product; class UpdateProductPrice { public function __construct(string $newPrice, string $currency, Product\Product $product) { $this->newPrice = Product\Price::fromString($newPrice, $currency); $this->product = $product; } public function newPrice() { return $this->newPrice; } public function product() { return $this->product; } }
27. Robert Bašić ~ ZGPHP #78 After CQRS (ii) <?php namespace App\Product\CommandHandler; use App\Product\Command; class UpdateProductPrice { public function handle(Command\UpdateProductPrice $command) { $product = $command->product(); $newPrice = $command->newPrice(); if ($product->onSale()) { throw new \Exception("Can't update price of products that are on sale!"); } $product->updatePrice($newPrice); $this->repository->save($product); } }
28. Robert Bašić ~ ZGPHP #78 CQRS, the good
29. Robert Bašić ~ ZGPHP #78 CQRS, the good • Smaller classes
30. Robert Bašić ~ ZGPHP #78 CQRS, the good • Smaller classes • Separated responsibilities
31. Robert Bašić ~ ZGPHP #78 CQRS, the good • Smaller classes • Separated responsibilities • Faster writes and reads
32. Robert Bašić ~ ZGPHP #78 CQRS, the good • Smaller classes • Separated responsibilities • Faster writes and reads • Easier database queries
33. Robert Bašić ~ ZGPHP #78 CQRS, the bad
34. Robert Bašić ~ ZGPHP #78 CQRS, the bad • More classes
35. Robert Bašić ~ ZGPHP #78 CQRS, the bad • More classes • Translation
36. Robert Bašić ~ ZGPHP #78 CQRS, the bad • More classes • Translation • Complex syncing
37. Robert Bašić ~ ZGPHP #78 CQRS, the bad • More classes • Translation • Complex syncing • Eventual consistency
38. Robert Bašić ~ ZGPHP #78 Service Bus
39. Robert Bašić ~ ZGPHP #78 What is a service bus?
40. Robert Bašić ~ ZGPHP #78 Types of service buses
41. Robert Bašić ~ ZGPHP #78 Types of service buses • Message type
42. Robert Bašić ~ ZGPHP #78 Types of service buses • Message type • Command bus
43. Robert Bašić ~ ZGPHP #78 Types of service buses • Message type • Command bus • Event bus
44. Robert Bašić ~ ZGPHP #78 Types of service buses • Message type • Command bus • Event bus • Query bus
45. Robert Bašić ~ ZGPHP #78 Service buses in PHP
46. Robert Bašić ~ ZGPHP #78 Service buses in PHP • Varying support for message types
47. Robert Bašić ~ ZGPHP #78 Service buses in PHP • Varying support for message types • Tactician
48. Robert Bašić ~ ZGPHP #78 Service buses in PHP • Varying support for message types • Tactician • SimpleBus
49. Robert Bašić ~ ZGPHP #78 Service buses in PHP • Varying support for message types • Tactician • SimpleBus • Prooph Service Bus
50. Robert Bašić ~ ZGPHP #78 Command Bus
51. Robert Bašić ~ ZGPHP #78 Command Bus
52. Robert Bašić ~ ZGPHP #78 Commands
53. Robert Bašić ~ ZGPHP #78 Commands • Messages about user intention
54. Robert Bašić ~ ZGPHP #78 Commands • Messages about user intention • CreateProduct, PutProductOnSale
55. Robert Bašić ~ ZGPHP #78 Commands • Messages about user intention • CreateProduct, PutProductOnSale • Name reveals use case
56. Robert Bašić ~ ZGPHP #78 Commands • Messages about user intention • CreateProduct, PutProductOnSale • Name reveals use case • One command, one action
57. Robert Bašić ~ ZGPHP #78 Dispatching commands, HTTP <?php class UpdatePriceAction { public function __invoke(Request $request) { $product = $this->getProduct($request->get('productid')); $command = new UpdateProductPrice( $request->get('price'), $request->get('currency'), $product ); $this->commandBus->dispatch($command); } private function getProduct($productId): Model\Product }
58. Robert Bašić ~ ZGPHP #78 Dispatching commands, CLI <?php class UpdatePriceCli { public function __invoke(Input $input) { $product = $this->getProduct($input->get('productid')); $command = new UpdateProductPrice( $input->get('price'), $input->get('currency'), $product ); $this->commandBus->dispatch($command); } private function getProduct($productId): Model\Product }
59. Robert Bašić ~ ZGPHP #78 A command is always valid <?php namespace App\Product\Command; use App\Product; class UpdateProductPrice { public function __construct(string $newPrice, string $currency, Product\Product $product) { $this->newPrice = Product\Price::fromString($newPrice, $currency); $this->product = $product; } public function newPrice() { return $this->newPrice; } public function product() { return $this->product; } }
60. Robert Bašić ~ ZGPHP #78 Command handlers <?php namespace App\Product\CommandHandler; use App\Product\Command; class UpdateProductPrice { public function handle(Command\UpdateProductPrice $command) { $product = $command->product(); $newPrice = $command->newPrice(); if ($product->onSale()) { throw new \Exception("Can't update price of products that are on sale!"); } $product->updatePrice($newPrice); $this->repository->save($product); } }
61. Robert Bašić ~ ZGPHP #78 Command buses in PHP
62. Robert Bašić ~ ZGPHP #78 Command buses in PHP • Tactician, SimpleBus, Prooph Service Bus
63. Robert Bašić ~ ZGPHP #78 Command buses in PHP • Tactician, SimpleBus, Prooph Service Bus • Differ in creation and configuration
64. Robert Bašić ~ ZGPHP #78 Command buses in PHP • Tactician, SimpleBus, Prooph Service Bus • Differ in creation and configuration • Similar usage
65. Robert Bašić ~ ZGPHP #78 Command buses in PHP • Tactician, SimpleBus, Prooph Service Bus • Differ in creation and configuration • Similar usage • Plugins, middlewares
66. Robert Bašić ~ ZGPHP #78 Event Bus
67. Robert Bašić ~ ZGPHP #78 Event Bus
68. Robert Bašić ~ ZGPHP #78 Events
69. Robert Bašić ~ ZGPHP #78 Events • Messages about past events
70. Robert Bašić ~ ZGPHP #78 Events • Messages about past events • After a command was handled
71. Robert Bašić ~ ZGPHP #78 Events • Messages about past events • After a command was handled • ProductCreated, ProductPriceUpdated
72. Robert Bašić ~ ZGPHP #78 Events • Messages about past events • After a command was handled • ProductCreated, ProductPriceUpdated • Once dispatched, can’t be stopped
73. Robert Bašić ~ ZGPHP #78 Dispatching events <?php namespace App\Product\CommandHandler; use App\Product; class UpdateProductPrice { public function handle(Product\Command\UpdateProductPrice $command) { /** ... snip ... **/ $this->repository->save($product); $event = new Product\Event\ProductPriceUpdated( (int) $product->id(), (double) $oldPrice, (double) $newPrice ); $this->eventBus->dispatch($event); } }
74. Robert Bašić ~ ZGPHP #78 An event is always valid <?php namespace App\Product\Event; class ProductPriceUpdated { public function __construct(int $productId, double $oldPrice, double $newPrice) { $this->productId = $productId; $this->oldPrice = $oldPrice; $this->newPrice = $newPrice; } public function productId() { return $this->productId; } public function oldPrice() { return $this->oldPrice; } public function newPrice() { return $this->newPrice; } }
75. Robert Bašić ~ ZGPHP #78 Event listeners <?php namespace App\Product\EventListener; use App\Product; class NotifyAboutPriceDrop { public function handle(Product\Event\ProductPriceUpdated $event) { if ($event->oldPrice() <= $event->newPrice()) { return; } $product = $this→repository→get($productId); $command = new Product\Command\SendPriceDecreaseEmail($product); $this->commandBus->dispatch($command); } }
76. Robert Bašić ~ ZGPHP #78 Event buses in PHP
77. Robert Bašić ~ ZGPHP #78 Event buses in PHP • SimpleBus, Prooph Service Bus
78. Robert Bašić ~ ZGPHP #78 Event buses in PHP • SimpleBus, Prooph Service Bus • Differ in creation and configuration
79. Robert Bašić ~ ZGPHP #78 Event buses in PHP • SimpleBus, Prooph Service Bus • Differ in creation and configuration • Similar usage
80. Robert Bašić ~ ZGPHP #78 Event buses in PHP • SimpleBus, Prooph Service Bus • Differ in creation and configuration • Similar usage • Plugins, middlewares
81. Robert Bašić ~ ZGPHP #78 Query Bus
82. Robert Bašić ~ ZGPHP #78 Query Bus
83. Robert Bašić ~ ZGPHP #78 Queries
84. Robert Bašić ~ ZGPHP #78 Queries • Not the same as database queries
85. Robert Bašić ~ ZGPHP #78 Queries • Not the same as database queries • A query is a question
86. Robert Bašić ~ ZGPHP #78 Queries • Not the same as database queries • A query is a question • LatestProductsCreated, ProductsOnSale
87. Robert Bašić ~ ZGPHP #78 Queries • Not the same as database queries • A query is a question • LatestProductsCreated, ProductsOnSale • Answers from read models
88. Robert Bašić ~ ZGPHP #78 Dispatching queries <?php class SalesReportAction { public function __invoke(Request $request) { $query = new ProductsBoughtInTimeframe( $request->get('from'), $request->get('to') ); $products = $this->queryBus->dispatch($query); // pass $products to template for displaying ... } }
89. Robert Bašić ~ ZGPHP #78 A query is always valid <?php namespace App\Product\Query; class ProductsBoughtInTimeframe { public function __construct(string $from, string $to) { $this->from = new \DateTimeImmutable($from); $this->to = new \DatetTimeImmutable($to); } public function from(): \DatetTimeImmutable { return $this->from; } public function to(): \DatetTimeImmutable { return $this->to; } }
90. Robert Bašić ~ ZGPHP #78 Query handlers <?php namespace App\Product\QueryHandler; use App\Product\Query; class ProductsBoughtInTimeframe { public function handle(Query\ProductsBoughtInTimeframe $query) { return $this->productsBoughtReadModel->fetch($query->from(), $query->to()); } }
91. Robert Bašić ~ ZGPHP #78 Query buses in PHP
92. Robert Bašić ~ ZGPHP #78 Query buses in PHP • Prooph Service Bus
93. Robert Bašić ~ ZGPHP #78 Query buses in PHP • Prooph Service Bus • Plugins
94. Robert Bašić ~ ZGPHP #78 Ready for the next project!
95. Robert Bašić ~ ZGPHP #78 Resources • CQRS Documents by Greg Young • SimpleBus by Matthias Noback • Prooph series by Robert Basic • perfi by Robert Basic
96. Robert Bašić ~ ZGPHP #78 Q&A Robert Bašić https://robertbasic.com/ @robertbasic
97. Robert Bašić ~ ZGPHP #78 Images used • http://www.globalgeeknews.com/2011/12/22/the-life-of-a-so ftware-engineer-comic/