Laravel Event Sourcing

Deck for Singapore Laravel Meetup on 22 Dec 2022.

Event Sourcing is architectural pattern that records all changes made to an application’s state, in the sequence in which the changes were originally applied.

This talk covers the concept of event sourcing in the context of Laravel using spatie's package, Laravel Event Sourcing, as a springboard for discussion.

Transcript

1. Event Sourcing Aurelia Lim @loribeanl Laravel Meet-up Dec 22 2022
2. I want to purchase a product products id name inventory_level = 3 3
3. I want to purchase a product products id name inventory_level = 3 2
4. I want to purchase a product products id name inventory_level = 3 2 Who made the change When the change occurred What/How was the change performed ? ? ? ? ? ? ? ?
5. I want to purchase a product products id name inventory_level = 3 3
6. I want to purchase a product products id name inventory_level = 3 2 Event ProductPurchased
7. I want to purchase a product Application State Event Log
8. I want to purchase a product Application State Event Log
9. I want to purchase a product Application State Event Log
10. I want to purchase a product Application State Event Log
11. Have you built a system that uses this concept?
12. Have you used a system that uses this concept?
13. Git Git Git
14. Git Git Git log blame checkout Who made the change When the change occurred What/How was the change performed
15. TLDR - each event is a transaction, and our application state can be derived from the event store. Event Sourcing
16. It is an easy entry point into adopting the event sourcing architecture. Package built by spatie Laravel Event Sourcing
17. Components
18. Components Event event_store Projectors Aggregates Reactors
19. Events Event event_store
20. Events Event Atomic in nature Represents a fact that took place Each change is recorded in an append only store Immutable - they are our source of truth Current application state is derived from events event_store
21. Events Even though events are immutable, but their e ff ects can be altered by later events.
22. Events Product Purchased Event Even though events are immutable, but their e ff ects can be altered by later events. products id name inventory_level
23. Events Product Purchased Event Even though events are immutable, but their e ff ects can be altered by later events. products id name inventory_level Product Restocked Event products id name inventory_level
24. <?php declare(strict_types=1); namespace App\Events; use Spatie\EventSourcing\StoredEvents\ShouldBeStored; class ProductPurchased extends ShouldBeStored { public $queue = 'purchase'; public function __construct( public readonly int $productId, public readonly int $quantity, ) { } }
25. <?php declare(strict_types=1); namespace App\Events; use Spatie\EventSourcing\StoredEvents\ShouldBeStored; class ProductRestocked extends ShouldBeStored { public function __construct( public readonly int $productId, public readonly int $quantity, ) { } }
27. Projectors Similar to event listeners. Transform the events into a format that is usable for our application Projectors
28. Projectors Projections should be treated as temporary and disposable. This is one of their key bene f its as they can be destroyed, reimagined, and recreated at will; they should not be considered the source of truth. Projectors
29. <?php declare(strict_types=1); namespace App\Projectors; use App\Events\ProductPurchased; use App\Events\ProductRestocked; use App\Models\Product; use App\Models\ProductPurchaseByDate; use Illuminate\Contracts\Queue\ShouldQueue; use Spatie\EventSourcing\EventHandlers\Projectors\Projector; class ProductInventoryProjector extends Projector implements ShouldQueue { public function onProductPurchased(ProductPurchased $event) { // Retrieve the product that was purchased $product = Product::find($event->productId); // Update the product's stock quantity $product->decrement('stock', $event->quantity); $product->save(); } public function onProductRestocked(ProductRestocked $event) { // Retrieve the product that was restocked $product = Product::find($event->productId); // Update the product's stock quantity $product->increment(‘inventory_level', $event->quantity); $product->save(); } }
30. <?php declare(strict_types=1); namespace App\Projectors; use App\Events\ProductPurchased; use App\Events\ProductRestocked; use App\Models\Product; use App\Models\ProductPurchaseByDate; use Illuminate\Contracts\Queue\ShouldQueue; use Spatie\EventSourcing\EventHandlers\Projectors\Projector; class ProductInventoryProjector extends Projector implements ShouldQueue { public function onProductPurchased(ProductPurchased $event) { // Retrieve the product that was purchased $product = Product::find($event->productId); // Update the product's inventory quantity $product->decrement(‘inventory_level', $event->quantity); $product->save(); } public function onProductRestocked(ProductRestocked $event) { // Retrieve the product that was restocked $product = Product::find($event->productId); // Update the product's stock quantity $product->decrement('stock', $event->quantity); $product->save(); } }
31. <?php declare(strict_types=1); namespace App\Providers; use App\Projectors\ProductInventoryProjector; use Illuminate\Support\ServiceProvider; use Spatie\EventSourcing\Facades\Projectionist; class EventSourcingServiceProvider extends ServiceProvider { public function register() { Projectionist::addProjector(ProductInventoryProjector::class); } }
32. <?php declare(strict_types=1); namespace App\Http\Controllers; use App\Events\ProductPurchased; use App\Http\Controllers\Controller; use Illuminate\Http\JsonResponse; class ProductPurchaseController extends Controller { public function __invoke(PurchaseRequest $request): JsonResponse { event(new ProductPurchased($request->product_id, $request->quantity)); return new JsonResponse([ 'data' => [ 'message' => 'product purchased', ], ]); } }
34. You have one unread message 1
36. Hi Lori We need to implement product analytics We need to provide meaningful insights on consumer behaviour. What products are most popular? What time period are consumers buying the most? 2:30PM
38. Ok, Let’s do it! 2:30PM
39. <?php declare(strict_types=1); namespace App\Projectors; use App\Events\ProductPurchased; use App\Events\ProductRestocked; use App\Models\Product; use App\Models\ProductPurchaseByDate; use Illuminate\Contracts\Queue\ShouldQueue; use Spatie\EventSourcing\EventHandlers\Projectors\Projector; class ProductInventoryProjector extends Projector implements ShouldQueue { public function onProductPurchased(ProductPurchased $event) { // Retrieve the product that was purchased $product = Product::find($event->productId); // Update the product's inventory quantity $product->decrement(‘inventory_level', $event->quantity); $product->save(); //Store some consumer analytics ProductPurchaseByDate::firstOrCreate( [ 'date' => $event->createdAt()->toDateString(), 'merchant_id' => $product->merchant_id, 'product_id' => $product->id, ], )->increment('purchase_count'); } public function onProductRestocked(ProductRestocked $event) { // Retrieve the product that was restocked $product = Product::find($event->productId); // Update the product's stock quantity $product->decrement('stock', $event->quantity); $product->save(); } }
41. ╭─[Aurelias-MBP] as aurelialim in ~/Sites/example-event-sourcing using node v19.2.0 01:29:07 ╰──➤ sail artisan event-sourcing:replay Are you sure you want to replay events to all projectors? (yes/no) [yes]: > yes Replaying 6 events... 6/6 [▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓] 100% All done! ~4s (base)
42. ProductPurchased Event event_store ProductPurchased event 1 ProductPurchased event 2 ProductPurchased event 3 I want to purchase a product API call to purchase a product ProductInventory Projector Products Id name Inventory
43. Aggregates Aggregates
44. Aggregates An aggregate is a class that helps you to make decisions based on events that happened in the past. Aggregates
45. <?php declare(strict_types=1); namespace App\Aggregates; use App\Events\ProductPurchased; use App\Reactors\PopularProductIdentified; use Spatie\EventSourcing\AggregateRoots\AggregateRoot; class ProductInventoryAggregate extends AggregateRoot { private $productPurchasedCount = 0; // we need to add this method to count the amount of this the product was purchased public function applyProductPurchased() { $this->productPurchasedCount++; } public function purchaseProduct(int $productId, int $quantity ) { $this->recordThat(new ProductPurchased($productId, $quantity)); if ($this->productPurchasedCount === 8) { $this->recordThat(new PopularProductIdentified($productId)); } return $this; } }
46. <?php declare(strict_types=1); namespace App\Http\Controllers; use App\Aggregates\ProductInventoryAggregate; use App\Http\Controllers\Controller; use Illuminate\Http\JsonResponse; class ProductPurchaseController extends Controller { public function __invoke(PurchaseRequest $request): JsonResponse { //instead of dispatching the event here, we let the aggregate do it for us // we used productId as the uuid $productId = $request->input('product_id'); ProductInventoryAggregate::retrieve($productId) ->purchaseProduct($productId, $request->quantity) ->persist(); } }
47. ProductPurchased Event event_store ProductPurchased event 1 ProductPurchased event 2 ProductPurchased event 3 I want to purchase a product API call to purchase a product ProductInventory Projector Products Id name Inventory ProductInventory Aggregate
48. Reactors Handle the side e ff ects of our applications. only get called when the original event f ires. Reactors
49. PopularProductIdenti f ied Event I want to purchase a product API call to purchase a product ProductInventory Aggregate Reactor Send an email to notify the merchant that their product has been purchased x amount of times
50. <?php declare(strict_types=1); namespace App\Reactors; use App\Events\PopularProductIdentified; use App\Mail\PopularProductIdentifiedMail; use Illuminate\Contracts\Queue\ShouldQueue; use Illuminate\Support\Facades\Mail; use Spatie\EventSourcing\EventHandlers\Reactors\Reactor; class PopularProductIdentifiedReactor extends Reactor implements ShouldQueue { public function __invoke(PopularProductIdentified $event) { $product = Product::find($event->productId); $email = $product->merchant->email; Mail::to($email)->send(new PopularProductIdentifiedMail($product)); } }
51. Key Bene f its Audit Time Travel Replay & Reshape Observability
52. Key Challenges Maintaining changing event schema Explanation Fatigue
54. Thank you!