Introduction
Every serious backend developer eventually faces the same problem: you need to make multiple changes to a database as part of a single business operation, and you need all of them to succeed or none of them to go through. Partial updates are worse than no updates at all - they leave your data in an inconsistent state that can be nearly impossible to debug in production.
This is not a new problem. Enterprise developers have been solving it for decades, and Martin Fowler documented the canonical solution in his 2002 book Patterns of Enterprise Application Architecture: the Unit of Work pattern.
In this article we are going to go deep on what Unit of Work is, why it exists, how it works internally, and how to build a clean, production-quality implementation from scratch in Python using only the standard library. By the end you will have a working implementation you can adapt to any project, and a solid understanding of how popular frameworks like SQLAlchemy and Django ORM implement this pattern under the hood.
The full source code is available on GitHub:
