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{
5 public function __construct(private PDO $pdo)
6 {
7 $this->pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
8 }
9 
10 public function placeOrder(int $customerId, array $lineItems): int
11 {
12 $this->pdo->beginTransaction();
13 
14 try {
15 $insertOrder = $this->pdo->prepare(
16 'INSERT INTO orders (customer_id, status, created_at) VALUES (?, ?, NOW())'
17 );
18 $insertOrder->execute([$customerId, 'pending']);
19 $orderId = (int) $this->pdo->lastInsertId();
20 
21 $insertItem = $this->pdo->prepare(
22 'INSERT INTO order_items (order_id, sku, quantity, unit_price) VALUES (?, ?, ?, ?)'
23 );
24 $decrementStock = $this->pdo->prepare(
25 'UPDATE products SET stock = stock - ? WHERE sku = ? AND stock >= ?'
26 );
27 
28 foreach ($lineItems as $item) {
29 $insertItem->execute([$orderId, $item['sku'], $item['qty'], $item['price']]);
30 $decrementStock->execute([$item['qty'], $item['sku'], $item['qty']]);
31 
32 if ($decrementStock->rowCount() === 0) {
33 throw new RuntimeException("Insufficient stock for SKU {$item['sku']}");
34 }
35 }
36 
37 $this->pdo->commit();
38 
39 return $orderId;
40 } catch (Throwable $e) {
41 $this->pdo->rollBack();
42 throw $e;
43 }
44 }
45}
01 / 01
STEP 01

Walkthrough

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

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