事件驅動架構（EDA）專注於解耦系統，並透過回應事件使系統更加靈活、可擴展和可維護。在 PHP 中，EDA 中經常使用的兩個重要模式是事件溯源和命令查詢職責分離（CQRS）。這是使用 PHP 實作它們的逐步指南，以及實作範例。
指令：
活動：
讀取模型:
建立目錄結構：
event-driven-php/
├── src/
│ ├── Commands/
│ ├── Events/
│ ├── Handlers/
│ ├── Models/
│ └── ReadModels/
├── tests/
└── vendor/
安裝依賴項（例如 symfony/event-dispatcher）：
composer require symfony/event-dispatcher
指令代表改變狀態的動作。範例：PlaceOrderCommand.php。
// src/Commands/PlaceOrderCommand.php
class PlaceOrderCommand
{
public string $orderId;
public string $customerId;
public function __construct(string $orderId, string $customerId)
{
$this->orderId = $orderId;
$this->customerId = $customerId;
}
}
事件描述了系統中發生的事情。範例：OrderPlacedEvent.php。
// src/Events/OrderPlacedEvent.php
class OrderPlacedEvent
{
public string $orderId;
public string $customerId;
public function __construct(string $orderId, string $customerId)
{
$this->orderId = $orderId;
$this->customerId = $customerId;
}
}
命令處理程序執行實際的業務邏輯並引發事件。範例：PlaceOrderHandler.php。
// src/Handlers/PlaceOrderHandler.php
use Symfony\Component\EventDispatcher\EventDispatcher;
class PlaceOrderHandler
{
private EventDispatcher $eventDispatcher;
public function __construct(EventDispatcher $eventDispatcher)
{
$this->eventDispatcher = $eventDispatcher;
}
public function handle(PlaceOrderCommand $command)
{
// Business logic (e.g., check stock, validate order)
// Emit the event
$event = new OrderPlacedEvent($command->orderId, $command->customerId);
$this->eventDispatcher->dispatch($event, 'order.placed');
}
}
事件處理程序偵聽特定事件並更新讀取模型。範例：OrderProjection.php。
// src/ReadModels/OrderProjection.php
class OrderProjection
{
private array $orders = [];
public function onOrderPlaced(OrderPlacedEvent $event)
{
// Save or update read model with necessary data
$this->orders[$event->orderId] = [
'orderId' => $event->orderId,
'customerId' => $event->customerId,
'status' => 'placed'
];
}
public function getOrder(string $orderId)
{
return $this->orders[$orderId] ?? null;
}
}
use Symfony\Component\EventDispatcher\EventDispatcher;
// Bootstrapping the system
$dispatcher = new EventDispatcher();
$orderProjection = new OrderProjection();
// Register event listeners
$dispatcher->addListener('order.placed', [$orderProjection, 'onOrderPlaced']);
// Create the command and command handler
$command = new PlaceOrderCommand('123', 'cust_001');
$handler = new PlaceOrderHandler($dispatcher);
// Handle the command (Place the order)
$handler->handle($command);
// Query the read model for the order
$order = $orderProjection->getOrder('123');
print_r($order);
輸出：
Array
(
[orderId] => 123
[customerId] => cust_001
[status] => placed
)
對於完整的事件來源，您還需要實作事件儲存將事件儲存到資料庫。
class EventStore
{
private array $storedEvents = [];
public function append(Event $event)
{
$this->storedEvents[] = $event;
}
public function getEventsForAggregate(string $aggregateId): array
{
return array_filter($this->storedEvents, function($event) use ($aggregateId) {
return $event->aggregateId === $aggregateId;
});
}
}
此範例示範了 CQRS 和 Event Sourcing 在 PHP 中的簡單應用。透過這些模式，您可以建立可擴展且可維護的系統，同時提供強大的可審核性和靈活的讀取/寫入處理。該架構可以隨著額外的投影、更複雜的事件處理以及訊息佇列或第三方通知等外部整合而成長。
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