DTO and Response Class Guide

Use this skill when creating or modifying DTO files in the dto/ folder.

Input DTO (Request)

import { IsDateString, IsEnum, IsNotEmpty, IsOptional, IsString, Length } from 'class-validator'; import { IsE164 } from 'src/app.utils';

import { EntityEnum } from '../entity.enums';

export class CreateEntityDto { @IsNotEmpty() @IsString() requiredField!: string;

@IsOptional() @IsString() @Length(1, 30) optionalField?: string;

@IsOptional() @IsDateString() dateField?: string;

@IsOptional() @IsEnum(EntityEnum) enumField?: EntityEnum; }

Input DTO Rules

Use class-validator decorators

• @IsNotEmpty() : Required fields

• @IsOptional() : Optional fields

• @IsString() , @IsNumber() , @IsBoolean() : Type validation

• @IsEnum() : Enum value validation

• @Length() : String length limits

• @IsDateString() : ISO 8601 date strings

Field Declaration

• Required fields: ! (definite assignment assertion)

• Optional fields: ? (optional)

Custom Decorators

• Phone numbers: @IsE164() (E.164 format validation)

• Define additional decorators in app.utils.ts as needed

Naming Conventions

• Find: Find{Entity}Dto

• Create: Create{Entity}Dto

• Update: Update{Entity}Dto

• Other: {Action}{Entity}Dto

Output Response Class

import { Expose } from 'class-transformer';

import { EntityEnum } from '../entity.enums';

export class FindEntityRes { @Expose() id!: string;

@Expose() name!: string;

@Expose() enumField!: EntityEnum;

@Expose() createdAt!: Date; }

Output Response Rules

@Expose() decorator is required

• Use @Expose() on all fields to expose

• Works with excludeExtraneousValues: true option

Naming Conventions

• Find: Find{Entity}Res

• Create: Create{Entity}Res

• Update: Update{Entity}Res

• Other: {Action}{Entity}Res

Entity → Response Transformation

import { mapTo } from '../app.utils';

// Usage in controller return mapTo(FindEntityRes, entity);

DTO/Response Same File Pattern

Define in same file when DTO and Response are closely related (e.g., update API):

// update-entity.dto.ts import { Expose } from 'class-transformer'; import { IsOptional, IsString, Length } from 'class-validator';

export class UpdateEntityDto { @IsOptional() @IsString() @Length(0, 30) name?: string; }

export class UpdateEntityRes { @Expose() id!: string;

@Expose() name!: string; }

mapTo Utility

Transformation function defined in app.utils.ts :

import { type ClassConstructor, plainToInstance } from 'class-transformer';

export function mapTo<T, I>(type: ClassConstructor<T>, instance: I): T { return plainToInstance(type, instance, { excludeExtraneousValues: true, }); }

Custom Validator Pattern

import { applyDecorators } from '@nestjs/common'; import { Matches } from 'class-validator';

export function IsE164(): PropertyDecorator { return applyDecorators( Matches(/^+[1-9]\d{1,14}$/, { message: '전화번호는 E.164을 준수해야 합니다.', }), ); }

File Structure

src/{module}/dto/ ├── create-{entity}.dto.ts ├── update-{entity}.dto.ts ├── find-{entity}.dto.ts └── index.ts # barrel export

index.ts (Barrel Export)

export * from './create-entity.dto'; export * from './update-entity.dto'; export * from './find-entity.dto';

ValidationPipe Configuration

Global pipe setup in main.ts :

app.useGlobalPipes( new ValidationPipe({ whitelist: true, // Remove undefined fields forbidNonWhitelisted: true, // Error on undefined fields transform: true, // Auto type transformation }), );