Enterprise Design Patterns in Python: Repository & Unit of Work — Real-World E-Commerce Example

Enterprise Design Patterns in Python: Repository & Unit of Work 🐍🏗️ Series: Enterprise Application Architecture | Source: Fowler's EAA Catalog | Code: GitHub Repository 🧠 What Are Enterprise Design Patterns? Martin Fowler's Patterns of Enterprise Application Architecture (2002) is one of the most influential books in software engineering. It documents recurring architectural solutions — patterns — that solve common problems in enterprise systems: how to organize domain logic, how to talk to databases, how to handle transactions, and more. In this article, we'll explore two of the most powerful and widely-used patterns from that catalog: Pattern Category Core Purpose Repository Data Source Abstracts data access behind a collection-like interface Unit of Work Data Source Tracks object changes and commits them as a single transaction These two patterns work beautifully together — and you'll see exactly why with a real-world example. 🛒 The Problem: An E-Commerce Order System Imagine you're building a backend for an online store. When a customer places an order: A new Order is created Each Product 's stock is decremented A Payment record is registered If any of these steps fail midway, the entire operation should roll back — no partial state. This is exactly the problem the Unit of Work pattern solves, and the Repository pattern makes it all cleanly testable. 📁 Repository Pattern Definition "A Repository mediates between the domain and data mapping layers using a collection-like interface for accessing domain objects." — Martin Fowler, PoEAA The Repository acts as an in-memory collection of domain objects. Your business logic never knows if it's talking to PostgreSQL, SQLite, or even a mock list — it just calls .add() , .get() , .list() . Domain Model # models.py from dataclasses import dataclass , field from typing import List from uuid import uuid4 @dataclass class Product : id : str name : str price : float stock : int @dataclass class OrderItem : product_id : str qua