class-validator Migration

tsgonest migrate converts class-validator DTO classes into TypeScript interfaces with branded types from @tsgonest/types. This page explains how each decorator is handled and what to watch for.

Class-to-Interface Conversion

Any file that imports from class-validator is processed. Each class (that isn't a NestJS framework class or ORM entity) is converted to an interface.

Before

import { IsEmail, IsNotEmpty, MinLength, IsOptional } from 'class-validator';

export class CreateUserDto {
  @IsEmail()
  @IsNotEmpty()
  email: string;

  @MinLength(6)
  password: string;

  @IsOptional()
  @IsNotEmpty()
  nickname?: string;
}

After

import { tags } from '@tsgonest/types';

export interface CreateUserDto {
  email: string & tags.Email & tags.MinLength<1>;
  password: string & tags.MinLength<6>;
  nickname?: string & tags.MinLength<1>;
}

Decorator Mapping Table

Constraint Decorators (mapped to branded types)

Behavior Decorators (removed, functionality handled by tsgonest)

Recognized but no branded type equivalent

These decorators are removed without adding a branded type. The validation is recognized but has no direct @tsgonest/types counterpart:

@IsJSON, @IsTimeZone, @IsCreditCard, @IsPhoneNumber, @IsHexColor, @IsMACAddress, @IsPort, @IsMimeType, @IsSemVer, @IsAlpha, @IsAlphanumeric, @IsNumberString, @IsBase64, @IsMongoId, @IsCurrency, @Contains, @NotContains, @IsHash, @IsLatitude, @IsLongitude, @IsLatLong

Unknown decorators

Custom validators (e.g., @IsUniqueName()) are flagged as TODOs in the migration report. The decorator is left in place so your code still compiles.

class-transformer Handling

tsgonest migrate also processes class-transformer decorators found on properties:

Mapped Types (OmitType, PickType, etc.)

Classes that extend OmitType(), PickType(), PartialType(), or IntersectionType() cannot be converted to interfaces — interfaces can't extend function calls. These classes are kept as classes, but their class-validator decorators are still stripped and branded types are added.

// Before
export class UpdateUserDto extends PickType(CreateUserDto, ['email']) {
  @IsNotEmpty()
  email: string;
}

// After — remains a class, decorators stripped, types updated
export class UpdateUserDto extends PickType(CreateUserDto, ['email']) {
  email: string & tags.MinLength<1>;
}

The @nestjs/swagger import for mapped-type helpers is automatically rewritten to @nestjs/mapped-types when no other swagger imports remain.

Skipped Classes

The following classes are detected and skipped entirely (not converted):

NestJS Framework Classes

Classes with any of these decorators are skipped: @Controller, @Module, @Injectable, @Guard, @Interceptor, @Pipe, @Filter

ORM Entity Classes

Classes with any of these decorators are skipped: @Entity, @Schema, @Table, @Document, @Model, @ViewEntity, @ChildEntity, @Embeddable

Entity classes often use class-validator decorators alongside ORM decorators. Since entities have their own lifecycle and aren't DTOs, they're left unchanged.

Non-class-validator Files

Files that don't import from class-validator are skipped entirely.

What Needs Manual Review

After migration, check the tsgonest-migrate-report.md for:

• Unknown decorators — Custom validators that couldn't be mapped automatically
• @Exclude properties — Decide whether to use Omit<>, separate types, or @tsgonest/types exclusion
• Complex @Transform patterns — Only trim(), toLowerCase(), and toUpperCase() are auto-mapped
• @IsIn(['a', 'b']) constraints — Consider using TypeScript union types ('a' | 'b') instead