NestJS Complete Guide

# NestJS Complete Guide NestJS is a progressive Node.js framework for building efficient, reliable, and scalable server-side applications. ## Architecture NestJS uses a modular architecture inspired by Angular. Each module encapsulates a bounded context of related functionality. ```typescript @Module({ imports: [DatabaseModule], controllers: [UsersController], providers: [UsersService], exports: [UsersService], }) export class UsersModule {} ``` ## Providers and Dependency Injection ```typescript @Injectable() export class UsersService { constructor( @InjectRepository(User) private readonly userRepo: Repository, ) {} async findAll(): Promise { return this.userRepo.find(); } } ``` ## Guards and Interceptors Guards handle authentication and authorization. Interceptors handle cross-cutting concerns like logging and caching. ```typescript @Injectable() export class AuthGuard implements CanActivate { canActivate(context: ExecutionContext): boolean { const request = context.switchToHttp().getRequest(); return !!request.user; } } ``` ## Microservices NestJS supports various transport layers including TCP, Redis, NATS, and gRPC for building distributed systems.