NestJS ta yi amfani da decorators ta yaya?

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Accepted Answer

NestJS an gina shi kusan **TypeScript decorators** — matakai na musamman masu prefix na `@` waɗanda suke haɗa **metadata** zuwa azuzuwan, hanyoyin, da sigogi. NestJS yana karanta wannan metadata (ta hanyar reflection) don haɗa routing, dependency injection, validation, da kari a hanya mai bayani. Decorators suna jiya a kuɗi.

## Azuzuwan decorators — ayyana matsayin azuzuwa

```ts
@Controller("users")     // this class is a CONTROLLER, prefix /users
export class UsersController {}

@Injectable()            // this class is a PROVIDER (injectable)
export class UsersService {}

@Module({ ... })         // this class is a MODULE
export class UsersModule {}
```

Azuzuwan decorators suna ayyana abin da azuzuwa *ne* a gida na NestJS (controller, provider, module) da kuma sa shi.

## Hanyoyin decorators — taɓa bakin hanya da aiki

```ts
@Get()                   // GET request handler
@Post()                  // POST handler
@Get(":id")              // GET /users/:id
@HttpCode(204)           // set the response status code
@UseGuards(AuthGuard)    // apply a guard to this route
@UseInterceptors(LoggingInterceptor)
findAll() {}
```

## Parameter decorators — cire bayanan bukatun

```ts
findOne(
  @Param("id") id: string,       // route parameter
  @Query("sort") sort: string,   // query string
  @Body() dto: CreateUserDto,    // request body
  @Headers("auth") auth: string, // header
) {}
```

Parameter decorators suna ja daidai bayanan da kuka bukata daga bukatun — babu ba manual `req` parsing ba.

## Mallaki/validation decorators (akan DTOs)

```ts
export class CreateUserDto {
  @IsEmail()                     // validation rules (class-validator)
  email: string;

@IsString()
  @MinLength(8)
  password: string;
}
```

## Me yasa decorators? Bayani a gida

```text
Decorators attach METADATA that NestJS reads at runtime (via reflection) to:
  ✓ Register routes (@Get, @Controller)
  ✓ Wire dependency injection (@Injectable, @Inject)
  ✓ Apply guards/interceptors/pipes (@UseGuards, etc.)
  ✓ Validate input (@IsEmail, @IsString)
→ Behavior is declared WHERE it applies, concisely and readably.
```

## Jiya na yau

```ts
// you can create your own — e.g. extract the current user from the request
export const CurrentUser = createParamDecorator((data, ctx) =>
  ctx.switchToHttp().getRequest().user
);
// usage: findProfile(@CurrentUser() user: User) {}
```

## Me ya shafi

Decorators shine kayar syntactic da ta bayyana NestJS — duk jiya shi wa shi ne da su aka tsara, saboda haka fahimtar yadda suke aiki shine mahimmanci ga karantawa da rubutu na kowane NestJS code.

Suna ba **bayani**, hanyar tunani na metadata: maimakon ummarar setup, kuna sa alamar azuzuwan, hanyoyin, da sigogi don ayyana routing (`@Controller`, `@Get`), dependency injection (`@Injectable`), jiya-tsawar jiya (`@UseGuards`, `@UseInterceptors`), da validation (`@IsEmail`) daidai inda suke aiki — gajere da karewa.

Wannan metadata-via-reflection hanya (wannan ra'ayi iri daya a bayan Angular da Java/Spring annotations) shi ne abin da ke ba NestJS launin daidai, tsarare.

Sanin kategorishi (azuzuwa, hanya, parameter, mallaki decorators), sanin waɗanda aka saba, da kuma iya yin jiya decorators shine mahimmanci NestJS fluency — decorators shine yadda kusan kowa bayani aka bayyana, wanda zai sa su ɗaya daga farko da mahimmancin lokacin fahimtar jiya.