decorator-patterns

NestJS Decorator Patterns

NestJS is decorator-driven. Knowing which decorator does what — and how they compose — prevents most "weird DI / weird routing" bugs.

Required tsconfig

{
  "compilerOptions": {
    "experimentalDecorators": true,
    "emitDecoratorMetadata": true
  }
}

emitDecoratorMetadata is what makes runtime introspection (and class-validator/class-transformer) work. Never disable.

reflect-metadata polyfill must be imported once at the top of main.ts:

import 'reflect-metadata';

(NestJS does this implicitly via @nestjs/core, but if you write a script that uses decorators outside the Nest app, import it manually.)

Class-level decorators

@Controller(prefix)

@Controller('users')                            // routes prefixed /users
@Controller({ path: 'users', version: '1' })    // versioned: /v1/users (with VersioningType.URI)
export class UsersController {}

@Injectable(options?)

@Injectable()                                   // singleton (default)
@Injectable({ scope: Scope.REQUEST })           // per-request
export class MyService {}

@Module(...)

@Module({ imports, controllers, providers, exports })
export class UsersModule {}

@Global()

@Global()
@Module({ providers: [...], exports: [...] })
export class LoggerModule {}

Use sparingly — see nest-conventions.

Method-level: HTTP routing

@Get()                          // GET /users
@Get(':id')                     // GET /users/:id
@Post()
@Put(':id')
@Patch(':id')
@Delete(':id')
@All('debug')                   // any method
@Head()
@Options()

Route options

@HttpCode(204)                  // override default status (200/201)
@Header('Cache-Control', 'no-store')
@Redirect('https://example.com', 301)
@Render('user-profile')         // for view engines (rare in API-only)

Versioning

@Controller({ path: 'users', version: ['1', '2'] })
@Version('2')                   // override at method level
@Get()
findV2() {}