API versioning and project structure

Model answer. Versioning lets you make breaking changes (renaming a field, changing a response shape) without breaking apps that still use the old contract.

Common approaches:

• URL path: /api/v1/students (most common; easy to see and cache).
• Header: Accept: application/vnd.example.v2+json (cleaner URLs, harder to test by hand).
• Query string: ?version=2 (simple, but easy to forget).

Version only for breaking changes; adding an optional field is not one. Announce deprecations and keep the old version alive for a set period.

A maintainable structure separates concerns:

src/
  app.js            express app: middleware, routers, error handler
  server.js         starts listening (keeps app testable)
  config/           environment variables, validated at start-up
  routes/v1/        routers: URL → controller
  controllers/      read the request, call a service, shape the response
  services/         business rules, no req/res
  models/ or db/    database queries
  middleware/       auth, validation, rate limiting
  utils/
tests/

Keeping HTTP details out of services makes them reusable from jobs, queues and tests.