Migrating from .NET to NestJS: Why I Decided to Stop Rewriting and Embrace the Legacy Code

Uchkun Rakhimov — Fri, 23 Jan 2026 22:09:28 +0000

Rewriting a project from scratch is every developer's dream—and often, a business’s nightmare. Recently, I found myself at the center of this exact dilemma.

The Backstory: A Failed Giant

The project was a massive CRM built with .NET (C#). After over a year of development and significant investment, the project was stalled. It was riddled with bugs, unfinished features, and a codebase that the original developers no longer wanted to touch.

The business owner decided to revive it and started looking for a new team. That’s where I came in. As a Node.js/NestJS developer, my mission was clear: relocate, join the new team (PM, Frontend, and myself), and rebuild the entire backend from scratch in NestJS.

The Strategy: How I Started the "Great Migration"

I didn’t want to go in blind. To understand the complexity, I used Cursor AI to dissect the C# logic. My plan was pragmatic:

Keep the Database: I stuck with the existing Postgres schema to avoid data migration headaches.
Prisma to the Rescue: I ran npx prisma db pull to instantly generate my NestJS models from the existing DB.
API Parity: I kept every endpoint name, request body, and error response identical to the original so the Frontend wouldn't have to change a single line of code.

The Realization: Breaking the "New is Always Better" Bias

Two weeks into the rewrite, something unexpected happened. After spending days reading the C# code to replicate it in NestJS, I started understanding it.

I began to see the patterns, the lifecycle of the .NET services, and specifically, where the previous team had tripped up. I realized that the core logic wasn't "bad"—it was just misunderstood and poorly maintained.

I had a choice: spend months rebuilding what already existed, or take a shortcut that could save the business.

The Pivot: Pitching the "Stay" to Stakeholders

I went to the founders with a risky proposal:
"I understand the C# codebase now. Instead of spending months rewriting this in NestJS, let me fix the existing backend. We’ll save time, money, and launch much faster."

Their response was simple: "If you can handle the responsibility, go for it."

Lessons Learned (So Far)

I am currently working within that same .NET project. I’ve cleared the major bugs, stabilized the core, and most importantly, I'm learning more than I ever would have by staying in my comfort zone.

My takeaways from this journey:

AI as a Language Bridge: Tools like Cursor AI are game-changers for understanding foreign codebases. They turn "reading code" into "having a conversation" with the logic.
The "Rewrite" Trap: Sometimes we want to rewrite because we're afraid of someone else's mess. But fixing that mess is often the more professional (and profitable) path.
Business First, Tech Second: Our job isn't just to write code in our favorite language; it's to solve problems.