NestJS Architecture Guide
Demo Creator
@seed-creator · muallif
The Module System
NestJS organizes code into modules that declare providers, controllers, imports, and exports. Modules are singletons — each is instantiated once per application lifecycle.
A well-structured NestJS app reads like a dependency graph: each module clearly states what it needs and what it exposes.
Providers and Dependency Injection
Any class decorated with @Injectable() can be injected. NestJS resolves the dependency graph at bootstrap time — circular dependencies fail loudly rather than silently.
Prefer constructor injection over property injection for testability. Constructor-injected dependencies are visible in unit tests without reflection.
Guards and the Request Lifecycle
Guards run before controllers and decide whether the request proceeds. Use them for authentication (verify the token is valid) and authorization (verify the token owner has the required role).
@Injectable()export class AuthGuard implements CanActivate { async canActivate(ctx: ExecutionContext): Promise<boolean> { const req = ctx.switchToHttp().getRequest<Request>(); const token = extractBearerToken(req); if (!token) throw new UnauthorizedException(); req.user = await this.firebase.verifyIdToken(token); return true; }}
Always extract from the HTTP request directly — guards run per-request, not per-module.
Layered Architecture
Controllers parse DTOs and delegate to services. Services contain business logic and call repositories. Repositories own all DB queries. This separation makes each layer independently testable.
6 ta izoh
Tizimga kiring izoh qoldirish uchun.
This landed at exactly the right time for me — the pull-quote is going straight into my notes.
Glad it helped! That line took a few rewrites to get right.
Same here. Any chance of a follow-up that goes a level deeper?
The callout halfway through saved me a debugging session this week.
Would love a section on the trickier edge cases.
+1 to that — the edge cases are where this stuff earns its keep.