# Nestjs Controllers Services

> Controller/Service separation and Custom Decorators. Use when defining NestJS controllers, services, or custom parameter decorators. (triggers: **/*.controller.ts, **/*.service.ts, Controller, Injectable, ExecutionContext, createParamDecorator)

- Skill: `comeonoliver/nestjs-controllers-services` (Agent Skill)
- Install (CLI): `npx skillmds@latest add comeonoliver/nestjs-controllers-services`
- Raw SKILL.md: https://api.skillmd.com/api/skills/comeonoliver/nestjs-controllers-services/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: AI & ML
- Author: ComeOnOliver (https://skillmd.com/u/comeonoliver)
- Updated: 2026-09-08
- Page: https://skillmd.com/skills/comeonoliver/nestjs-controllers-services

---


# NestJS Controllers & Services Standards

## **Priority: P0 (FOUNDATIONAL)**

Layer separation standards and dependency injection patterns for NestJS applications.

## Controllers

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

  ```typescript
  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**:
  - **Automation**: Use the `@nestjs/swagger` CLI plugin (`nest-cli.json`) to auto-detect DTO properties without manual `@ApiProperty()` tags.

## Interceptors (Response Mapping)

- **Standardization**: specific responses should be mapped in **Interceptors**, not Controllers.
  - Use `map()` to wrap success responses (e.g. `{ data: T }`).
  - Refer to **[API Standards](../nestjs-api-standards/SKILL.md)** for `PageDto` and `ApiResponse`.
  - Use `catchError()` to map low-level errors (DB constraints) to `HttpException` (e.g. `ConflictException`) _before_ they hit the global filter.

## Services & Business Logic

- **Singleton**: Default.
- **Stateless**: Do not store request-specific state in class properties unless identifying as `Scope.REQUEST`.

## Pipes & Validation

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

```typescript
@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 the entire injection chain request-scoped.