NestJS Controllers & Services Standards

Priority: P0 (CRITICAL)

Controllers

• Role: Handler only. Delegate all logic to Services.
• Context: ExecutionContext helpers (switchToHttp()) for platform-agnostic code.
• Custom Decorators:
• Avoid: @Request() req -> req.user (Not type-safe).
• Pattern: Create typed decorators like @CurrentUser(), @DeviceIp().

import { RequestWithUser } from 'src/common/interfaces/request.interface';

export const CurrentUser = createParamDecorator(
  (data: unknown, ctx: ExecutionContext): User => {
    const request = ctx.switchToHttp().getRequest<RequestWithUser>();
    return request.user;
  },
);

DTOs & Validation

• Strictness:
• whitelist: true: Strip properties without decorators.
• Critical: forbidNonWhitelisted: true: Throw error if unknown properties exist.
• Transformation:
• transform: true: Auto-convert primitives (String '1' -> Number 1) and instantiate DTO classes.
• Documentation:
• Swagger Plugin: @nestjs/swagger CLI plugin in nest-cli.json auto-detects DTO properties — no manual @ApiProperty().

Interceptors (Response Mapping)

• Map responses in Interceptors, not Controllers.
• map() wraps success responses (e.g. { data: T }).
• See API Standards for PageDto and ApiResponse.
• catchError() maps low-level errors (DB constraints) to HttpException (e.g. ConflictException) before global filter.

Services & Business Logic

• Singleton: Default.
• Stateless: No request-specific state in class properties unless Scope.REQUEST.

Pipes & Validation

• Global: Register ValidationPipe globally.
• Route Params: Fail fast. Always use ParseIntPipe, ParseUUIDPipe on all ID parameters.

@Get(':id')
findOne(@Param('id', ParseIntPipe) id: number) { ... }

Lifecycle Events

• Init: Use OnModuleInit for connection setup.
• Destroy: Use OnApplicationShutdown for cleanup. (Requires enableShutdownHooks()).

Anti-Patterns

• No business logic in controllers: Delegate everything to Services; controllers only parse and respond.
• No req.user access: Create typed @CurrentUser() decorator instead of accessing raw req.
• No REQUEST scope by default: Use SINGLETON; it makes entire injection chain request-scoped.

References

• Decorator, Pipe & Lifecycle Examples