CustomBodyValidationPipe.ts

import {
  ArgumentMetadata,
  BadRequestException,
  PipeTransform,
  ValidationPipe,
} from '@nestjs/common';
import { Product1, Product2 } from './dtos/create-product.dto';
import { plainToInstance } from 'class-transformer';
import { validate } from 'class-validator';

/** @see https://stackoverflow.com/questions/54057006/nestjs-validating-body-conditionally-based-on-one-property **/
export class ProductValidationPipe implements PipeTransform {
  async transform(value: any) {
    if (!value) {
      throw new BadRequestException('Invalid Request');
    }
    let dtoValidator: Product1 | Product2;
    if (value.type === 'PRODUCT_1') {
      dtoValidator = plainToInstance(Product1, value);
    }
    if (value.type === 'PRODUCT_2') {
      dtoValidator = plainToInstance(Product2, value);
    }
    const errors = await validate(dtoValidator);
    if (errors.length > 0) {
      const validationPipe = new ValidationPipe();
      const exceptionFactory = validationPipe.createExceptionFactory();
      throw exceptionFactory(errors);
    }
    return value;
  }
}