Question 1

TypeORM vs Prisma with Nest — practical trade-offs?

Accepted Answer

TypeORM: Active Record/Data Mapper, Nest module mature; Prisma: strong typing/DX, separate client lifecycle. Either can work — migrations, transactions, and testing matter more than brand. Know N+1 risks in both.

Question 2

Where should repositories live in Nest modules?

Accepted Answer

As providers in the feature module (or dedicated persistence adapter module), injected into services. Avoid controllers talking to ORM directly. Keep query details out of HTTP layer.

Question 3

How do you handle transactions in Nest services?

Accepted Answer

ORM transaction APIs / QueryRunner / Prisma $transaction; pass transactional client/unit-of-work through the use-case. Don't open transactions in controllers. Watch request-scoped pitfalls. Keep transactions short.

Question 4

N+1 queries in Nest resolvers/services — prevention?

Accepted Answer

Eager/join appropriately, DataLoader for GraphQL, and explicit query planning — never lazy-load in loops blindly. Log slow queries in staging. Review list endpoints for join strategies.

Question 5

Migrations in production Nest apps — best practices?

Accepted Answer

Expand/contract migrations, backward-compatible deploys, and never rely on synchronize in prod. CI runs migrations with locks. Document rollback. Separate schema from data migrations.

Question 6

Lead: multi-DB or CQRS read models with Nest?

Accepted Answer

Separate modules/connections for write vs read, async projections, and clear consistency expectations. Don't pretend every screen needs strong consistency. Own failure modes of projection lag.

ORM Concepts NestJS Interview Questions

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