nestjs class validator decorators and configs for when we don't necessarily want to skip validation if value is null. (create and update)

user.controller.ts

import {
  Controller,
  Post,
  Body,
  ValidationPipe,
  applyDecorators,
  Patch,
  UsePipes,
  Param,
  ParseIntPipe,
} from "@nestjs/common";
import { ApiProperty } from "@nestjs/swagger";
import { IsInt, IsNotEmpty, IsString, ValidateIf } from "class-validator";
import { PartialType } from "@nestjs/mapped-types";

function MayBeUndefined() {
  return applyDecorators(
    ValidateIf((_, value) => typeof value !== "undefined"),
  );
}

class CreateUserDto {
  @ApiProperty({
    type: String,
    required: true,
    nullable: false,
  })
  @IsNotEmpty()
  @IsString()
  name: string;

  @ApiProperty({
    type: Number,
    required: false,
    nullable: false,
  })
  @MayBeUndefined()
  @IsInt()
  age?: number;
}

class UpdateUserDto extends PartialType(CreateUserDto, {
  skipNullProperties: false,
}) {}

@UsePipes(
  new ValidationPipe({
    transform: true,
    whitelist: true,
    forbidNonWhitelisted: true,
  }),
)
@Controller("users")
export class UsersController {
  constructor() {}

  @Post()
  async createUser(
    @Body() body: CreateUserDto,
  ) {}

  @Patch(":id")
  async updateUser(
    @Param("id", ParseIntPipe) id: number,
    @Body() body: UpdateUserDto,
  ) {}
}