Tutorials System Design Tutorial
Unit of Work Pattern — Complete Guide
Unit of Work Pattern — Complete Guide: free step-by-step lesson with examples, common mistakes, and interview tips — part of System Design Tutorial on Toolliyo Academy.
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System Design Tutorial · Lesson 76 of 100
Unit of Work Pattern
Basics ✓ → Scale ✓ → Interview
Interview · 3 — Case studies · ~10 min · Module 8: Low-Level Design
What is this?
Unit of Work tracks a business transaction’s changes and commits them together — often wrapping a DB transaction.
Why should you care?
ShopNest placing an order may touch multiple entities that must commit atomically.
See it live — copy this example
Sketch the architecture on paper. These lessons focus on concepts and trade-offs.
uow.Start()
repoOrders.Add(...)
repoOutbox.Add(...)
uow.Commit() // one DB transaction
On error: Rollback()Run Example »
This lesson uses terminal or setup steps. Run commands on your computer — the live editor appears on coding lessons.
What happened?
- UoW ensures multiple repository calls share one transaction boundary.
- Align with outbox inserts for reliable events.
Practice next
- Wrap ShopNest place-order writes in one UoW/transaction.
- Include outbox row in the same commit.
- Rollback on payment precondition failures before commit.
- Measure transaction duration.
- Fail fast before opening UoW when validation fails.
Remember
One business action → one commit when possible. Pair with outbox. Keep external IO outside the DB transaction.
Atomic order+outbox
ShopNest UoW commits both together.
Outcome: No order without its event row.
Interview prep for this lesson
Practice these questions aloud after reading—each links to a full structured answer.
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