Article Medium - Enhanced validation in Nest.js - STEP-5

create-customer.dto.ts

import { Type } from 'class-transformer';
import { IsEmail, IsNotEmpty, ValidateNested } from 'class-validator';

class AddressCustomerType {
  @IsNotEmpty()
  city: string;

  @IsNotEmpty()
  address: string;
}

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

  @IsNotEmpty()
  password: string;

  @IsNotEmpty()
  @ValidateNested()
  @Type(() => AddressCustomerType)
  address: AddressCustomerType;
}

validation.filter.ts

export const exceptionFactory = (errors: ValidationError[]) => {
  const errorValidation = {};
  let errorMessages = [];
  const parseErrorMessage = (errObject, propertyKey) => {
    const isNested =
      typeof errObject?.children !== 'undefined' &&
      errObject?.children.length > 0;
    if (!isNested) {
      const messages = Object.values(errObject?.constraints);
      errorValidation[`${propertyKey}`] = [...messages];
      errorMessages.push(messages); // Default property message error
      return true;
    }
    errObject?.children.map((valChild) => {
      const nextPropertyKey = `${propertyKey}.${valChild.property}`;
      parseErrorMessage(valChild, nextPropertyKey);
    });
  };
  errors.forEach((err) => {
    parseErrorMessage(err, err.property);
  });
  errorMessages = errorMessages.flat(1); // Default property message error
  return new ValidationException(errorValidation, errorMessages);