Menene DTOs a cikin NestJS?

Question

Accepted Answer

A **DTO (Data Transfer Object)** shine ajami da ke bayyana **sifofin bayanan** da aka aika zuwa ko daga NestJS API - yawanci tsarin jikin bukatun. DTOs suna ba da noyayi, suna bayyana yarjejeniya mai bayyani ga ayyukan API, kuma (tare da kayan auna fasali) suna ba da damar auni mai sauri na shigarwa.

## Bayyana DTO

```ts
import { IsEmail, IsString, MinLength, IsOptional, IsInt, Min } from "class-validator";

export class CreateUserDto {
  @IsEmail()                    // must be a valid email
  email: string;

@IsString()
  @MinLength(8)                 // password at least 8 chars
  password: string;

@IsOptional()                 // optional field
  @IsInt()
  @Min(0)
  age?: number;
}
```

DTO shine ajami mai saukilili da ke bayyana bayanan da ake mamakin, tare da **kayan auni fasali** (daga `class-validator`) da ke taddatar da ƙa'idodin da kowane filin ya dace.

## Amfani da DTO a cikin controller

```ts
@Post()
create(@Body() dto: CreateUserDto) {     // the body is typed AND validated as CreateUserDto
  // dto is guaranteed to be valid here (with the validation pipe enabled)
  return this.usersService.create(dto);
}
```

`@Body() dto: CreateUserDto` yana ba da noyayi ga jikin bukatun kuma - tare da tubali na auni da aka kunna - yana auni mai sauri kafin maimakon aiki ya gudna.

## Kunna auni mai sauri

```ts
// main.ts — turn on the global validation pipe
app.useGlobalPipes(new ValidationPipe({
  whitelist: true,              // strip properties NOT in the DTO (security)
  forbidNonWhitelisted: true,   // reject requests with extra unknown properties
  transform: true,              // auto-transform payloads to DTO instances + convert types
}));
```

Tare da `ValidationPipe`, NestJS yana auni jikin inawa a gida DTOs na ƙa'idoji na auni - yana ba da kuskure na 400 tare da yadda fa'in takaddama bai yi nasara ba, kafin kodunka ya gudna.

## DTOs da Entities

```text
DTO    → the shape of data crossing the API boundary (request/response contract)
Entity → the database model (e.g. a TypeORM entity / Prisma model)
→ Keep them SEPARATE: the API contract shouldn't be coupled to the DB schema.
  (A CreateUserDto has password+email; the User entity has id, timestamps, etc.)
```

DTOs ba su dace da sinadari na database - suna wakilta abin da API ke karba/bada, da'a daga ajali na ciki.

## Bambantarwa da sake amfani

```ts
import { PartialType } from "@nestjs/mapped-types";
// derive an UpdateUserDto where all fields are optional — no duplication
export class UpdateUserDto extends PartialType(CreateUserDto) {}
```

## Dalilin da ya sa yana da muhimma

DTOs shine mahimman mahimmancin NestJS da ke kawo da noyayi, yarjejeniya mai bayyani ga API, da auni mai sauri zuwa ayyukan aiki.

Suna bayyana daidai abin da aiki ke karba (sifar bukatun), na ba ku noyayi na lokacin karantawa kuma suna aiki azaman kwantar jiya mai rainin kanta.

Mahallin abin, tare da `class-validator` na ƙa'idoji na auni da `ValidationPipe`, suna ba da damar **auni mai sauri na shigarwa** — bukatun da ba daidai ba ko masu hasana za'a ki kar daga sai da zai zuwa ga ilimin kasuwanci, wanda ke da mahimma ga tsaro da iko (zabin `whitelist` kuma yana cire kadawai abubuwa da ba a budata).

Jimagewa DTOs, yadda za'a ƙara ƙa'idoji na auni, yadda za'a kunna tubali na auni, da mahimmancin mahimma na **sa DTOs kewayi daga sinadarin database** (kawo daga yarjejeniya ta API daga ajali na ciki) shine tushe don gina tsaro, tsare jiya, da madaidaicin NestJS APIs.

DTOs suna bayyana a kusan kowane aiki da ke karba shigarwa, na sa su da mahimma, ilimin aiki na kowa.