using-nestjs-pipes-guards-interceptors

name	using-nestjs-pipes-guards-interceptors
description	Applies pipes, guards, and interceptors for cross-cutting concerns in NestJS — validation, auth, transformation, logging, caching. Use when implementing auth, response shaping, observability, or any concern that should not live in controllers.
license	MIT

Using NestJS Pipes, Guards, Interceptors

When to use

• Implementing authentication/authorization
• Adding logging, caching, response shaping
• Cross-cutting concerns that shouldn't live in controllers

Core rules

1. Pipes: transform/validate input (use ValidationPipe globally)
2. Guards: authenticate/authorize requests (AuthGuard, RolesGuard)
3. Interceptors: transform responses, log, cache, timeout (ClassSerializerInterceptor)
4. Implement as @Injectable() classes, register globally or at controller/route level
5. No logic in controllers that belongs in these cross-cutting components

Reference shape (TypeScript)

Auth Guard

@Injectable()
export class AuthGuard implements CanActivate {
  canActivate(context: ExecutionContext): boolean {
    const req = context.switchToHttp().getRequest();
    return !!req.user; // Simplified
  }
}

Roles Guard

@Injectable()
export class RolesGuard implements CanActivate {
  constructor(private reflector: Reflector) {}

  canActivate(context: ExecutionContext): boolean {
    const requiredRoles = this.reflector.get<string[]>('roles', context.getHandler());
    if (!requiredRoles) return true;
    const { user } = context.switchToHttp().getRequest();
    return requiredRoles.some(role => user.roles.includes(role));
  }
}

Examples — Do

@UseGuards(AuthGuard, RolesGuard)
@Get('admin')
@Roles('admin')
getAdminData() { ... }

Examples — Don't

// ❌ Auth logic in controller
@Get('profile')
getProfile(@Req() req) {
  if (!req.user) throw new UnauthorizedException(); // Move to guard
}

Checklist

• Pipes for validation/transformation
• Guards for auth/roles
• Interceptors for cross-cutting (logging, caching)
• Registered globally or per-controller

See reference/cross-cutting-patterns.md for full patterns.