E-Commerce Backend

Quick Introduction

E-Commerce Backend is a single PHP idea you'll use in almost every backend project.

In this lesson you learn only e-commerce backend — not five topics at once. By the end you can write a small working example and explain it in an interview.

We connect each lesson to our course projects: Login System, Blog CMS, REST API, Inventory, Employee Management, and E-Commerce Backend.

Business Problem

You're building the E-Commerce Backend. After a user signs in, you need e-commerce backend working correctly before storing data or showing a dashboard.

Without understanding E-Commerce Backend, the team ships bugs: wrong totals, broken sessions, or type errors that only appear in production. This lesson fixes that with one clear pattern you can copy into your project today.

Core Concept

• E-Commerce Backend is one focused idea — learn it before mixing with other PHP topics.
• Use it in PHP 8.3+ with declare(strict_types=1); at the top of every file.
• Our course project (E-Commerce Backend) uses e-commerce backend in real handlers.
• Run small scripts with php file.php after each change — don't just read.
• Interviewers ask for a one-minute explanation plus a tiny code sample.

Syntax

Core syntax for E-Commerce Backend. Every keyword below appears in production PHP — Laravel and Symfony use the same primitives under the hood.

declare(strict_types=1);

Keywords: declare · strict_types · namespace

Step-by-Step Example

Run this script locally. Change one value, run again, and watch what changes.

<?php
declare(strict_types=1);

namespace Shop;

final readonly class CartItem {
    public function __construct(public string $sku, public int $qty, public int $priceCents) {}
}

final class CheckoutService {
    public function __construct(private InventoryService $inventory, private PaymentGateway $pay) {}

    public function checkout(int $customerId, CartItem ...$items): string {
        foreach ($items as $item) {
            $this->inventory->reserve($item->sku, $item->qty);
        }
        $total = array_sum(array_map(fn(CartItem $i) => $i->priceCents * $i->qty, $items));
        return $this->pay->charge($customerId, $total);
    }
}

interface InventoryService { public function reserve(string $sku, int $qty): void; }
interface PaymentGateway { public function charge(int $customerId, int $cents): string; }

Line by line

1. — part of the e-commerce backend example; run the file to see the result.
2. declare(strict_types=1); — turns on strict type checking for this file.
3. namespace Shop; — part of the e-commerce backend example; run the file to see the result.
4. final readonly class CartItem { — part of the e-commerce backend example; run the file to see the result.
5. public function __construct(public string $sku, public int $qty, public int $priceCents) {} — part of the e-commerce backend example; run the file to see the result.

User #42 (user@example.com) balance $19.99

Real-World Example

In the E-Commerce Backend, e-commerce backend appears in a single request handler — not spread across ten files. Keep the example small, test it with php, then paste the pattern into your project branch.

<?php
declare(strict_types=1);

// TODO: E-Commerce Backend exercise for E-Commerce Backend