php 45 lines · 8 steps

Atomic order placement with PDO transactions

A repository writes an order, its items, and stock decrements as one all-or-nothing database transaction.

Explained by highlit

Intermediate transactions prepared-statements atomicity error-handling repository-pattern

1<?php
2 
3final class OrderRepository
4{
  public function __construct(private PDO $pdo)
  {
      $this->pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
  }
9 
  public function placeOrder(int $customerId, array $lineItems): int
  {
      $this->pdo->beginTransaction();
13 
      try {
          $insertOrder = $this->pdo->prepare(
              'INSERT INTO orders (customer_id, status, created_at) VALUES (?, ?, NOW())'
          );
          $insertOrder->execute([$customerId, 'pending']);
          $orderId = (int) $this->pdo->lastInsertId();
20 
          $insertItem = $this->pdo->prepare(
              'INSERT INTO order_items (order_id, sku, quantity, unit_price) VALUES (?, ?, ?, ?)'
          );
          $decrementStock = $this->pdo->prepare(
              'UPDATE products SET stock = stock - ? WHERE sku = ? AND stock >= ?'
          );
27 
          foreach ($lineItems as $item) {
              $insertItem->execute([$orderId, $item['sku'], $item['qty'], $item['price']]);
              $decrementStock->execute([$item['qty'], $item['sku'], $item['qty']]);
31 
              if ($decrementStock->rowCount() === 0) {
                  throw new RuntimeException("Insufficient stock for SKU {$item['sku']}");
              }
          }
36 
          $this->pdo->commit();
38 
          return $orderId;
      } catch (Throwable $e) {
          $this->pdo->rollBack();
          throw $e;
      }
  }
45}

01 / 01

STEP 01

Walkthrough

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Three takeaways

1Wrapping related writes in a transaction guarantees they all succeed or all roll back, leaving no half-finished orders.
2A conditional UPDATE plus rowCount() enforces business invariants like stock availability at the database level.
3Preparing a statement once and executing it per item reuses the query plan and keeps values safely bound.

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