Article Medium - Enhanced validation in Nest.js - STEP-4

main.ts

import { NestFactory } from '@nestjs/core';
import { AppModule } from './app.module';
import { ValidationPipe } from '@nestjs/common';
import {
  ValidationFilter,
  exceptionFactory,
} from './exceptions/validation.filter';

async function bootstrap() {
  const app = await NestFactory.create(AppModule);
  app.useGlobalPipes(new ValidationPipe());
  app.useGlobalFilters(new ValidationFilter());
  app.useGlobalPipes(
    new ValidationPipe({
      skipMissingProperties: false, // If Null/Undefined Value , still validated
      transform: true, // Transform plain object to DTO Type/Classes
      exceptionFactory,
    }),
  );
  await app.listen(3000);
}
bootstrap();

validation.filter.ts

import {
  ArgumentsHost,
  BadRequestException,
  Catch,
  ExceptionFilter,
  ValidationError,
} from '@nestjs/common';

export class ValidationException extends BadRequestException {
  public messageErrors;
  public validationErrors;

  constructor(validationErrors: any, messageErrors?: any) {
    super();
    this.messageErrors = messageErrors;
    this.validationErrors = validationErrors;
  }
}

@Catch(ValidationException)
export class ValidationFilter implements ExceptionFilter {
  catch(exception: ValidationException, host: ArgumentsHost): any {
    const ctx = host.switchToHttp();
    const response = ctx.getResponse();
    return response.status(400).json({
      message: exception.messageErrors,
      error: 'Bad Request',
      statusCode: 400,
      data: exception.validationErrors,
    });
  }
}

export const exceptionFactory = (errors: ValidationError[]) => {
  const errorValidation = {};
  let errorMessages = [];
  const parseErrorMessage = (errObject) => {
    const propertyKey = errObject.property;
    const messages = Object.values(errObject?.constraints);
    errorValidation[`${propertyKey}`] = [...messages];
    errorMessages.push(messages); // Default property message error
    return true;
  };
  errors.forEach((err) => {
    parseErrorMessage(err);
  });
  errorMessages = errorMessages.flat(1); // Default property message error
  return new ValidationException(errorValidation, errorMessages);
};