Repository Pattern

Quick Introduction

Repository Pattern is a single PHP idea you'll use in almost every backend project.

In this lesson you learn only repository pattern — 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 Inventory Management. After a user signs in, you need repository pattern working correctly before storing data or showing a dashboard.

Without understanding Repository Pattern, 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

• Repository Pattern 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 (Inventory Management) uses repository pattern 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 Repository Pattern. 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 App\Repository;

interface ProductRepository {
    public function findBySku(string $sku): ?array;
    /** @return list<array> */
    public function findByCategory(string $category, int $limit = 20): array;
}

final class PdoProductRepository implements ProductRepository {
    public function __construct(private \PDO $pdo) {}

    public function findBySku(string $sku): ?array {
        $stmt = $this->pdo->prepare('SELECT * FROM products WHERE sku = :sku LIMIT 1');
        $stmt->execute(['sku' => $sku]);
        return $stmt->fetch(\PDO::FETCH_ASSOC) ?: null;
    }

    public function findByCategory(string $category, int $limit = 20): array {
        $stmt = $this->pdo->prepare('SELECT id, sku, name, price FROM products WHERE category = :cat LIMIT :lim');
        $stmt->bindValue(':cat', $category);
        $stmt->bindValue(':lim', $limit, \PDO::PARAM_INT);
        $stmt->execute();
        return $stmt->fetchAll();
    }
}

Line by line

1. — part of the repository pattern example; run the file to see the result.
2. declare(strict_types=1); — turns on strict type checking for this file.
3. namespace App\Repository; — part of the repository pattern example; run the file to see the result.
4. interface ProductRepository { — part of the repository pattern example; run the file to see the result.
5. public function findBySku(string $sku): ?array; — part of the repository pattern example; run the file to see the result.

{"status":"ok"}

Real-World Example

In the Inventory Management, repository pattern 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: Repository Pattern exercise for Inventory Management