Create a separate datasource.ts file for the TypeORM CLI that does not depend on the NestJS app module. Generate migrations with migration:generate, apply with migration:run, and roll back with migration:revert. Never use synchronize: true in production — use migrations exclusively.

Separate datasource and migration workflow

Migration workflow best practices:

1
Never use synchronize: true in production — it can drop columns and tables destructively.
2
Keep a separate datasource.ts for the TypeORM CLI so it works independently of the NestJS app module.
3
Always implement down() — rollbacks are critical for safe deployments and hotfixes.
4
Commit all migration files to version control — they are the source of truth for schema history.
5
Use migrationsRun: true in the NestJS TypeORM config to auto-apply pending migrations on startup.

Difficulty: 5/10

Topics: migration generation, migration execution, migration strategy

Scenario Questions

0-2 years experience

1
You need to add a new column to an existing User entity. Walk me through the steps you’d take to create and apply a TypeORM migration in a NestJS project.
2
If you run npm run migration:run and it reports 'No pending migrations', but you know you added a new entity field, what could be causing that and how would you fix it?

2-5 years experience

1
During a feature rollout, a migration fails halfway on production because of a NOT NULL constraint. How would you diagnose and resolve the issue without causing downtime?
2
Explain why you might choose to write a migration manually instead of letting TypeORM generate it automatically, and give an example where the generated migration would be problematic.

5-8 years experience

1
Our service runs in a zero‑downtime deployment pipeline and serves traffic from multiple instances. How would you design a migration strategy using TypeORM in NestJS to ensure schema changes are applied safely across all instances?
2
We have a multi‑tenant database where each tenant has its own schema. How would you manage TypeORM migrations to handle schema versioning per tenant while keeping the codebase maintainable?

8+ years experience

1
Across several microservices that share a common database, how would you coordinate TypeORM migrations to avoid version drift and ensure consistent schema evolution across teams?
2
Describe a long‑term migration governance process you’d put in place for a large organization using NestJS and TypeORM, covering CI/CD integration, rollback procedures, and documentation.

Follow-up Questions

❓What challenges have you faced when a migration caused data loss, and how did you mitigate them?
❓How do you ensure migrations are idempotent and safe to run multiple times?
❓Can you talk about how you version‑control migration files alongside application code?