Order Placement

Place Order Service

namespace Magento\Checkout\Model;

class PlaceOrder
{
    public function __construct(
        private \Magento\Quote\Api\CartRepositoryInterface $cartRepository,
        private \Magento\Quote\Api\CartManagementInterface $cartManagement,
        private \Magento\Quote\Model\QuoteFactory $quoteFactory
    ) {}

    public function execute(int $cartId): int
    {
        $cart = $this->cartRepository->get($cartId);

        // Validate cart
        $this->validateCart($cart);

        // Reserve order ID
        $cart->reserveOrderId();

        // Convert quote to order
        $orderId = $this->cartManagement->placeOrder($cartId);

        return $orderId;
    }

    private function validateCart(\Magento\Quote\Api\Data\CartInterface $cart): void
    {
        if ($cart->getItemsCount() === 0) {
            throw new \Magento\Framework\Exception\LocalizedException(
                __('Cart is empty')
            );
        }

        if (!$cart->getShippingAddress()->getShippingMethod()) {
            throw new \Magento\Framework\Exception\LocalizedException(
                __('Shipping method not selected')
            );
        }

        if (!$cart->getPayment()->getMethod()) {
            throw new \Magento\Framework\Exception\LocalizedException(
                __('Payment method not selected')
            );
        }
    }
}

Inventory Reservation System

// Magento\InventoryReservation\Model\ReservationFactory
namespace Magento\Inventory\Api\ReservationServiceInterface;

interface ReservationServiceInterface
{
    /**
     * Create inventory reservation
     */
    public function create(
        string $sku,
        int $stockId,
        float $quantity,
        string $reservationId
    ): void;
}

Reservation During Order Placement

// During order creation, inventory is reserved
namespace Magento\Sales\Model\Service\Order;

class InventoryReservation
{
    public function __construct(
        private \Magento\Inventory\Api\ReservationServiceInterface $reservationService,
        private \Magento\Inventory\Api\StockResolverInterface $stockResolver
    ) {}

    public function reserve(
        \Magento\Sales\Api\Data\OrderInterface $order
    ): void {
        foreach ($order->getItems() as $item) {
            $stockId = $this->stockResolver->execute(
                $item->getWebsiteId()
            )->getStockId();

            $this->reservationService->create(
                $item->getSku(),
                $stockId,
                -$item->getQtyOrdered(),
                sprintf('order:%s:items:%s', $order->getIncrementId(), $item->getItemId())
            );
        }
    }
}

Reservation Cleanup

// Cancel reservation when order is cancelled
public function cancelReservation(\Magento\Sales\Api\Data\OrderInterface $order): void
{
    foreach ($order->getItems() as $item) {
        $this->reservationService->create(
            $item->getSku(),
            $stockId,
            $item->getQtyOrdered(), // Positive to release
            sprintf('order:%s:cancel', $order->getIncrementId())
        );
    }
}

Payment During Order Placement

namespace Magento\Quote\Model\QuoteManagement;

class PaymentProcessor
{
    public function process(
        \Magento\Quote\Model\Quote $quote,
        \Magento\Sales\Api\Data\OrderInterface $order
    ): void {
        $payment = $order->getPayment();
        $paymentMethod = $quote->getPayment()->getMethod();

        // Get payment method instance
        $method = $this->paymentMethodPool->getMethod($paymentMethod);

        // Process based on action type
        switch ($method->getConfigData('payment_action')) {
            case 'authorize':
                $method->authorize($payment, $order->getGrandTotal());
                break;
            case 'authorize_capture':
                $method->order($payment, $order->getGrandTotal());
                break;
        }

        // Set order status
        $order->setStatus($method->getConfigData('order_status'));
    }
}

Payment Error Handling

try {
    $orderId = $this->placeOrder->execute($cartId);
} catch (\Magento\Framework\Exception\PaymentException $e) {
    // Payment failed - restore inventory
    $this->inventoryReservation->cancelReservation($order);

    // Log error
    $this->logger->error('Payment failed: ' . $e->getMessage());

    throw new \Magento\Framework\Exception\LocalizedException(
        __('Payment processing failed: %1', $e->getMessage())
    );
} catch (\Exception $e) {
    // General error
    $this->logger->critical($e);
    throw $e;
}

Quote to Order Conversion

// Full order placement flow
public function placeOrder(int $cartId): int
{
    $cart = $this->cartRepository->get($cartId);

    // 1. Validate cart items
    $this->validateItems($cart);

    // 2. Reserve order ID
    $cart->reserveOrderId();

    // 3. Collect totals
    $cart->collectTotals();

    // 4. Create order from quote
    $order = $this->quoteToOrderConverter->convert($cart);

    // 5. Process payment
    $this->paymentProcessor->process($cart, $order);

    // 6. Reserve inventory
    $this->inventoryReservation->reserve($order);

    // 7. Save order
    $this->orderRepository->save($order);

    // 8. Send order confirmation email
    $this->orderEmailSender->send($order);

    // 9. Deactivate quote
    $cart->setIsActive(0)->save();

    return $order->getEntityId();
}

Guest Order Placement

// Guest order with email
POST /rest/V1/guest-carts/{cartId}/payment-information
{
    "paymentMethod": {
        "method": "checkmo"
    },
    "billingAddress": {
        "firstname": "Guest",
        "lastname": "Customer",
        "email": "guest@example.com",
        "street": ["123 Main St"],
        "city": "New York",
        "region_id": 43,
        "postcode": "10001",
        "country_id": "US",
        "telephone": "555-1234"
    }
}