Question 1

What is a Nest controller responsible for?

Accepted Answer

HTTP/transport mapping: routes, DTO binding, status codes — not business rules. Keep controllers thin; delegate to providers/services. Decorators declare method, path, pipes, and guards.

Question 2

How do @Param, @Query, @Body, and @Headers work together?

Accepted Answer

They extract typed pieces of the request into handler arguments, often with pipes for validation/transform. Prefer explicit DTOs over raw any. Combine with ValidationPipe. Avoid over-binding huge objects you don't need.

Question 3

Versioning APIs in Nest — approaches?

Accepted Answer

URI, header, or media-type versioning via built-in versioning options on the app and controllers. Pick one org standard. Don't mix casually. Plan deprecation windows for old versions.

Question 4

When should logic leave the controller?

Accepted Answer

As soon as there are rules, transactions, multi-step orchestration, or non-trivial mapping. Controllers that call three services and implement policy become untestable. Use application services/use-cases.

Question 5

Scenario: controller returns entities with password hashes. Fix?

Accepted Answer

Never return ORM entities directly — map to response DTOs/serializers and exclude sensitive fields. class-serializer interceptors help but explicit mappers are clearer. Add tests that fail on sensitive keys.

Question 6

Lead: conventions for public vs internal Nest controllers?

Accepted Answer

Separate modules/prefixes, stricter authz, OpenAPI tagging, and different rate limits/SLOs. Internal admin routes must not share casual guards. Document breaking-change policy. Generate clients from OpenAPI.

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