how to use OmitType from nestjs swagger

AI Response

OmitType from @nestjs/swagger is a utility function that allows you to create a new DTO (Data Transfer Object) by omitting specific properties from an existing DTO class.

Usage of OmitType

The OmitType function is useful when you want to create a subset of an existing DTO while excluding certain fields, particularly in request DTOs where some properties (e.g., id, createdAt, etc.) should not be included in user input.

Syntax

import { OmitType } from '@nestjs/swagger';

class BaseDto {
  id: number;
  createdAt: Date;
  updatedAt: Date;
  name: string;
  email: string;
}

class CreateUserDto extends OmitType(BaseDto, ['id', 'createdAt', 'updatedAt']) {}

Example Use Cases

1. Creating a DTO for a Create API

You might have a UserDto that represents a full user object with properties like id, createdAt, and updatedAt. However, when a user is being created, these fields should not be included in the request.

import { OmitType } from '@nestjs/swagger';

class UserDto {
  id: number;
  createdAt: Date;
  updatedAt: Date;
  name: string;
  email: string;
}

export class CreateUserDto extends OmitType(UserDto, ['id', 'createdAt', 'updatedAt']) {}

Here, CreateUserDto will only contain name and email properties.

2. Creating an Update DTO

For an update operation, you might want to allow only partial updates, omitting fields like id.

import { PartialType, OmitType } from '@nestjs/swagger';

class UserDto {
  id: number;
  name: string;
  email: string;
  createdAt: Date;
  updatedAt: Date;
}

export class UpdateUserDto extends PartialType(OmitType(UserDto, ['id', 'createdAt', 'updatedAt'])) {}

OmitType(UserDto, ['id', 'createdAt', 'updatedAt']): Removes id, createdAt, and updatedAt.
PartialType(...): Makes all properties optional.

Your Code Example

In your file action-required.dto.ts, you used OmitType like this:

export class ActionRequiredLogDtoRequest extends OmitType<
  ActionRequiredLogDto,
  ['createdTime']
> {}

This means ActionRequiredLogDtoRequest will inherit all properties from ActionRequiredLogDto, except createdTime, making it useful for request payloads where createdTime should not be provided.

Key Takeaways

OmitType(BaseDto, ['prop1', 'prop2']): Creates a DTO without specified properties.
Common Use Cases:

Create DTOs (omit id, createdAt, updatedAt).
Update DTOs (omit id, use PartialType for optional fields).

Used in NestJS Swagger for API documentation.