All aboard the Service Bus

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
   

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2. Robert Bašić ~ PHPSrbija #29
   A new project appears
   

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3. Robert Bašić ~ PHPSrbija #29
   Ready to build greatness
   

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4. Robert Bašić ~ PHPSrbija #29
   Your creation
   

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5. Robert Bašić ~ PHPSrbija #29
   // todo finish this
   

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6. Robert Bašić ~ PHPSrbija #29
   // refactor me later
   

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7. Robert Bašić ~ PHPSrbija #29
   // dirty hack to work around...
   

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8. Robert Bašić ~ PHPSrbija #29
   Same old story
   

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9. Robert Bašić ~ PHPSrbija #29
   Same old story
   ● An image gallery
   

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10. Robert Bašić ~ PHPSrbija #29
    Same old story
    ● An image gallery
    ● Multiple currencies
    

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11. Robert Bašić ~ PHPSrbija #29
    Same old story
    ● An image gallery
    ● Multiple currencies
    ● Coupons
    

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12. Robert Bašić ~ PHPSrbija #29
    Same old story
    ● An image gallery
    ● Multiple currencies
    ● Coupons
    ● Sales
    

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13. Robert Bašić ~ PHPSrbija #29
    Same old story
    ● An image gallery
    ● Multiple currencies
    ● Coupons
    ● Sales
    ● Reviews
    

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14. Robert Bašić ~ PHPSrbija #29
    Same old story
    ● An image gallery
    ● Multiple currencies
    ● Coupons
    ● Sales
    ● Reviews
    ● With images
    

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15. Robert Bašić ~ PHPSrbija #29
    Same old story
    ● An image gallery
    ● Multiple currencies
    ● Coupons
    ● Sales
    ● Reviews
    ● With images
    ● Old products
    

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16. Robert Bašić ~ PHPSrbija #29
    Same old story
    ● An image gallery
    ● Multiple currencies
    ● Coupons
    ● Sales
    ● Reviews
    ● With images
    ● Old products
    ● Warehousing
    

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17. Robert Bašić ~ PHPSrbija #29
    Been there, done that
    

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18. Robert Bašić ~ PHPSrbija #29
    Command Query Responsibility
    Segregation
    

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19. Robert Bašić ~ PHPSrbija #29
    CQRS
    

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20. Robert Bašić ~ PHPSrbija #29
    CQRS
    

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21. Robert Bašić ~ PHPSrbija #29
    CQRS
    ● Use cases
    

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22. Robert Bašić ~ PHPSrbija #29
    CQRS
    ● Use cases
    ● Separation of concerns
    

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23. Robert Bašić ~ PHPSrbija #29
    CQRS
    ● Use cases
    ● Separation of concerns
    ● Improved readability
    

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24. Robert Bašić ~ PHPSrbija #29
    CQRS
    ● Use cases
    ● Separation of concerns
    ● Improved readability
    ● Improved performance
    

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25. Robert Bašić ~ PHPSrbija #29
    Before CQRS
    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) { /* ... */ }
    }
    

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26. Robert Bašić ~ PHPSrbija #29
    After CQRS (i)
    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; }
    }
    

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27. Robert Bašić ~ PHPSrbija #29
    After CQRS (ii)
    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);
    }
    }
    

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28. Robert Bašić ~ PHPSrbija #29
    CQRS, the good
    

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29. Robert Bašić ~ PHPSrbija #29
    CQRS, the good
    ● Smaller classes
    

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30. Robert Bašić ~ PHPSrbija #29
    CQRS, the good
    ● Smaller classes
    ● Separated responsibilities
    

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31. Robert Bašić ~ PHPSrbija #29
    CQRS, the good
    ● Smaller classes
    ● Separated responsibilities
    ● Faster writes and reads
    

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32. Robert Bašić ~ PHPSrbija #29
    CQRS, the good
    ● Smaller classes
    ● Separated responsibilities
    ● Faster writes and reads
    ● Easier database queries
    

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33. Robert Bašić ~ PHPSrbija #29
    CQRS, the bad
    

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34. Robert Bašić ~ PHPSrbija #29
    CQRS, the bad
    ● More classes
    

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35. Robert Bašić ~ PHPSrbija #29
    CQRS, the bad
    ● More classes
    ● Translation
    

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36. Robert Bašić ~ PHPSrbija #29
    CQRS, the bad
    ● More classes
    ● Translation
    ● Complex syncing
    

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37. Robert Bašić ~ PHPSrbija #29
    CQRS, the bad
    ● More classes
    ● Translation
    ● Complex syncing
    ● Eventual consistency
    

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38. Robert Bašić ~ PHPSrbija #29
    Service Bus
    

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39. Robert Bašić ~ PHPSrbija #29
    What is a service bus?
    

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40. Robert Bašić ~ PHPSrbija #29
    Types of service buses
    

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41. Robert Bašić ~ PHPSrbija #29
    Types of service buses
    ● Message type
    

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42. Robert Bašić ~ PHPSrbija #29
    Types of service buses
    ● Message type
    ● Command bus
    

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43. Robert Bašić ~ PHPSrbija #29
    Types of service buses
    ● Message type
    ● Command bus
    ● Event bus
    

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44. Robert Bašić ~ PHPSrbija #29
    Types of service buses
    ● Message type
    ● Command bus
    ● Event bus
    ● Query bus
    

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45. Robert Bašić ~ PHPSrbija #29
    Service buses in PHP
    

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46. Robert Bašić ~ PHPSrbija #29
    Service buses in PHP
    ● Varying support for message types
    

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47. Robert Bašić ~ PHPSrbija #29
    Service buses in PHP
    ● Varying support for message types
    ● Tactician
    

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48. Robert Bašić ~ PHPSrbija #29
    Service buses in PHP
    ● Varying support for message types
    ● Tactician
    ● SimpleBus
    

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49. Robert Bašić ~ PHPSrbija #29
    Service buses in PHP
    ● Varying support for message types
    ● Tactician
    ● SimpleBus
    ● Prooph Service Bus
    

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50. Robert Bašić ~ PHPSrbija #29
    Command Bus
    

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51. Robert Bašić ~ PHPSrbija #29
    Command Bus
    

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52. Robert Bašić ~ PHPSrbija #29
    Commands
    

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53. Robert Bašić ~ PHPSrbija #29
    Commands
    ● Messages about user intention
    

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54. Robert Bašić ~ PHPSrbija #29
    Commands
    ● Messages about user intention
    ● CreateProduct, PutProductOnSale
    

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55. Robert Bašić ~ PHPSrbija #29
    Commands
    ● Messages about user intention
    ● CreateProduct, PutProductOnSale
    ● Name reveals use case
    

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56. Robert Bašić ~ PHPSrbija #29
    Commands
    ● Messages about user intention
    ● CreateProduct, PutProductOnSale
    ● Name reveals use case
    ● One command, one action
    

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57. Robert Bašić ~ PHPSrbija #29
    Dispatching commands, HTTP
    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
    }
    

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58. Robert Bašić ~ PHPSrbija #29
    Dispatching commands, CLI
    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
    }
    

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59. Robert Bašić ~ PHPSrbija #29
    A command is always valid
    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; }
    }
    

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60. Robert Bašić ~ PHPSrbija #29
    Command handlers
    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);
    }
    }
    

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61. Robert Bašić ~ PHPSrbija #29
    Command buses in PHP
    

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62. Robert Bašić ~ PHPSrbija #29
    Command buses in PHP
    ● Tactician, SimpleBus, Prooph Service Bus
    

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63. Robert Bašić ~ PHPSrbija #29
    Command buses in PHP
    ● Tactician, SimpleBus, Prooph Service Bus
    ● Differ in creation and configuration
    

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64. Robert Bašić ~ PHPSrbija #29
    Command buses in PHP
    ● Tactician, SimpleBus, Prooph Service Bus
    ● Differ in creation and configuration
    ● Similar usage
    

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65. Robert Bašić ~ PHPSrbija #29
    Command buses in PHP
    ● Tactician, SimpleBus, Prooph Service Bus
    ● Differ in creation and configuration
    ● Similar usage
    ● Plugins, middlewares
    

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66. Robert Bašić ~ PHPSrbija #29
    Event Bus
    

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67. Robert Bašić ~ PHPSrbija #29
    Event Bus
    

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68. Robert Bašić ~ PHPSrbija #29
    Events
    

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69. Robert Bašić ~ PHPSrbija #29
    Events
    ● Messages about past events
    

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70. Robert Bašić ~ PHPSrbija #29
    Events
    ● Messages about past events
    ● After a command was handled
    

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71. Robert Bašić ~ PHPSrbija #29
    Events
    ● Messages about past events
    ● After a command was handled
    ● ProductCreated, ProductPriceUpdated
    

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72. Robert Bašić ~ PHPSrbija #29
    Events
    ● Messages about past events
    ● After a command was handled
    ● ProductCreated, ProductPriceUpdated
    ● Once dispatched, can’t be stopped
    

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73. Robert Bašić ~ PHPSrbija #29
    Dispatching events
    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);
    }
    }
    

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74. Robert Bašić ~ PHPSrbija #29
    An event is always valid
    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; }
    }
    

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75. Robert Bašić ~ PHPSrbija #29
    Event listeners
    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);
    }
    }
    

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76. Robert Bašić ~ PHPSrbija #29
    Event buses in PHP
    

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77. Robert Bašić ~ PHPSrbija #29
    Event buses in PHP
    ● SimpleBus, Prooph Service Bus
    

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78. Robert Bašić ~ PHPSrbija #29
    Event buses in PHP
    ● SimpleBus, Prooph Service Bus
    ● Differ in creation and configuration
    

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79. Robert Bašić ~ PHPSrbija #29
    Event buses in PHP
    ● SimpleBus, Prooph Service Bus
    ● Differ in creation and configuration
    ● Similar usage
    

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80. Robert Bašić ~ PHPSrbija #29
    Event buses in PHP
    ● SimpleBus, Prooph Service Bus
    ● Differ in creation and configuration
    ● Similar usage
    ● Plugins, middlewares
    

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81. Robert Bašić ~ PHPSrbija #29
    Query Bus
    

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82. Robert Bašić ~ PHPSrbija #29
    Query Bus
    

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83. Robert Bašić ~ PHPSrbija #29
    Queries
    

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84. Robert Bašić ~ PHPSrbija #29
    Queries
    ● Not the same as database queries
    

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85. Robert Bašić ~ PHPSrbija #29
    Queries
    ● Not the same as database queries
    ● A query is a question
    

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86. Robert Bašić ~ PHPSrbija #29
    Queries
    ● Not the same as database queries
    ● A query is a question
    ● LatestProductsCreated, ProductsOnSale
    

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87. Robert Bašić ~ PHPSrbija #29
    Queries
    ● Not the same as database queries
    ● A query is a question
    ● LatestProductsCreated, ProductsOnSale
    ● Answers from read models
    

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88. Robert Bašić ~ PHPSrbija #29
    Dispatching queries
    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 ...
    }
    }
    

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89. Robert Bašić ~ PHPSrbija #29
    A query is always valid
    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;
    }
    }
    

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90. Robert Bašić ~ PHPSrbija #29
    Query handlers
    namespace App\Product\QueryHandler;
    use App\Product\Query;
    class ProductsBoughtInTimeframe {
    public function handle(Query\ProductsBoughtInTimeframe $query) {
    return $this->productsBoughtReadModel->fetch($query->from(), $query->to());
    }
    }
    

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91. Robert Bašić ~ PHPSrbija #29
    Query buses in PHP
    

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92. Robert Bašić ~ PHPSrbija #29
    Query buses in PHP
    ● Prooph Service Bus
    

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93. Robert Bašić ~ PHPSrbija #29
    Query buses in PHP
    ● Prooph Service Bus
    ● Plugins
    

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94. Robert Bašić ~ PHPSrbija #29
    Ready for the next project!
    

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95. Robert Bašić ~ PHPSrbija #29
    Resources
    ● CQRS Documents by Greg Young
    ● SimpleBus by Matthias Noback
    ● Prooph series by Robert Basic
    ● perfi by Robert Basic
    

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96. Robert Bašić ~ PHPSrbija #29
    Q&A
    Robert Bašić
    https://robertbasic.com/
    @robertbasic
    

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97. Robert Bašić ~ PHPSrbija #29
    Images used
    ● http://www.globalgeeknews.com/2011/12/22/the-life-of-a-so
    ftware-engineer-comic/
    

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