Apa iku pipe lan carane validasi bisa berjalan?

Question

Accepted Answer

**Pipe** yaiku kelas sing **ngubah utawa validasi** data input sadurunge tekan route handler. Iku berjalan ing argumen-argumen metode kontroler — ngubah (conto: string → number) utawa validasi (nolak data sing ora valid). Validasi ing NestJS dibangun ing sadhuwur pipe.

## Built-in transformation pipes

```ts
@Get(":id")
findOne(@Param("id", ParseIntPipe) id: number) {    // transforms "5" (string) → 5 (number)
  // id is guaranteed to be a number; non-numeric input → 400 error automatically
  return this.usersService.findOne(id);
}
// other built-ins: ParseBoolPipe, ParseUUIDPipe, ParseArrayPipe, DefaultValuePipe
```

Transformation pipe ngubah input dadi tipe sing bener (route params/query tansah string), gagal karo 400 yen pengubahan ora bisa.

## The ValidationPipe — automatic DTO validation

```ts
// enable globally in main.ts
app.useGlobalPipes(new ValidationPipe({
  whitelist: true,              // remove properties not declared in the DTO
  forbidNonWhitelisted: true,   // throw if unknown properties are present
  transform: true,              // turn plain objects into DTO instances, convert types
}));
```

```ts
// with a DTO using class-validator decorators:
export class CreateUserDto {
  @IsEmail() email: string;
  @MinLength(8) password: string;
}

@Post()
create(@Body() dto: CreateUserDto) {   // ValidationPipe validates the body automatically
  // if invalid → 400 with details, BEFORE this runs
}
```

`ValidationPipe` maca dekorator `class-validator` saka DTO lan validasi data masuk kanthi otomatis — bali detail 400 error yen gagal, supaya handler mung nampa data sing valid.

## How pipes fit in the request flow

```text
Request → ...middleware/guards/interceptors... → PIPES (transform/validate) → Handler
Pipes run JUST BEFORE the route handler, operating on its method arguments.
```

## Custom pipes

```ts
@Injectable()
export class TrimPipe implements PipeTransform {
  transform(value: any) {
    return typeof value === "string" ? value.trim() : value;   // custom transformation
  }
}
// usage: @Body(TrimPipe) ...
```

Sampeyan implementasi metode `transform()` `PipeTransform` kanggo logika validasi/pengubahan sing khusus.

## Applying pipes at different levels

```ts
@UsePipes(new ValidationPipe())      // method or controller level
@Param("id", ParseIntPipe)            // parameter level
app.useGlobalPipes(new ValidationPipe())   // global (most common for validation)
```

## Mengapa itu penting

Pipe yaiku fitur kunci NestJS kanggo nangani input kanthi aman, lan iku fondasi saka **sistem validasi** framework.

Paham iku penting amarga meh kabeh API endpoint kudu validasi lan ngubah input: transformation pipe (`ParseIntPipe`, lsp.) njamin parameter tipe bener, lan — paling penting — **`ValidationPipe`** digabung karo DTO nagamake validasi otomatis lan deklartif saka request body lawan aturan `class-validator`, nolak input sing ora valid utawa jahat karo kesalahan jelas *sadurunge* tekan logika bisnis.

Iku kritis kanggo keamanan (validasi/satinasi input sing ora dipercaya, copot properti sing ora dienteni) lan ketahanan (handler nampa mung data sing valid).

Ngerti carane ngaktifake global validation pipe karo pilihan sing masuk akal (`whitelist`, `transform`), nggunakake transformation pipe built-in, lan nulis pipe khusus yaiku mendasar kanggo bangun API NestJS sing aman lan terstruktur karo bener — pipe lan validasi yaiku konsep saben dina lan wajib ngerti ing framework.