Guide on how to create a custom response using class-validator in NestJS

Question

Guide on how to create a custom response using class-validator in NestJS

Is it feasible to customize the error response generated by class-validator in NestJs?

The default error message structure in NestJS looks like this:

{
    "statusCode": 400,
    "error": "Bad Request",
    "message": [
        {
            "target": {},
            "property": "username",
            "children": [],
            "constraints": {
                "maxLength": "username must be shorter than or equal to 20 characters",
                "minLength": "username must be longer than or equal to 4 characters",
                "isString": "username must be a string"
            }
        },
    ]
}

However, the external service interacting with my API requires a format closer to:

{
    "status": 400,
    "message": "Bad Request",
    "success": false,
    "meta": {
        "details": {
            "maxLength": "username must be shorter than or equal to 20 characters",
            "minLength": "username must be longer than or equal to 4 characters",
            "isString": "username must be a string"
        }
    }
}

javascript typescript nestjs class-validator

Answer 1

Answer №1

Nestjs offers built-in elements known as Exception filters, which allow you to customize your response in case of exceptions. For more information, refer to the documentation available here.

If you are looking to create your own filter, the code snippet below can be a useful reference.

import { ExceptionFilter, Catch, ArgumentsHost, BadRequestException } from '@nestjs/common';
import { Request, Response } from 'express';

@Catch(BadRequestException)
export class BadRequestExceptionFilter implements ExceptionFilter {
  catch(exception: BadRequestException, host: ArgumentsHost) {
    const ctx = host.switchToHttp();
    const response = ctx.getResponse<Response>();
    const request = ctx.getRequest<Request>();
    const status = exception.getStatus();

    response
      .status(status)
      // custom response manipulation can be done here
      .json({
        statusCode: status,
        timestamp: new Date().toISOString(),
        path: request.url,
      });
  }
}

Answer 2

Nestjs offers built-in elements known as Exception filters, which allow you to customize your response in case of exceptions. For more information, refer to the documentation available here.

If you are looking to create your own filter, the code snippet below can be a useful reference.

import { ExceptionFilter, Catch, ArgumentsHost, BadRequestException } from '@nestjs/common';
import { Request, Response } from 'express';

@Catch(BadRequestException)
export class BadRequestExceptionFilter implements ExceptionFilter {
  catch(exception: BadRequestException, host: ArgumentsHost) {
    const ctx = host.switchToHttp();
    const response = ctx.getResponse<Response>();
    const request = ctx.getRequest<Request>();
    const status = exception.getStatus();

    response
      .status(status)
      // custom response manipulation can be done here
      .json({
        statusCode: status,
        timestamp: new Date().toISOString(),
        path: request.url,
      });
  }
}

Answer 3

Answer №2

When creating your own ValidationPipe, you have the option to include a custom exceptionFactory.

new ValidationPipe({
      exceptionFactory: (errors) =>  new HttpException({ error: "BAD_REQUEST" }, 400)
})

The expected type for the first argument is a string, but it can also accept an object. As stated in the NestJS documentation:

If you want to customize only the message part of the JSON response body, provide a string in the response argument. If you wish to fully customize the JSON response body, pass an object as the response argument. Nest will serialize the object and return it as the JSON response body.

Answer 4

When creating your own ValidationPipe, you have the option to include a custom exceptionFactory.

new ValidationPipe({
      exceptionFactory: (errors) =>  new HttpException({ error: "BAD_REQUEST" }, 400)
})

The expected type for the first argument is a string, but it can also accept an object. As stated in the NestJS documentation:

If you want to customize only the message part of the JSON response body, provide a string in the response argument. If you wish to fully customize the JSON response body, pass an object as the response argument. Nest will serialize the object and return it as the JSON response body.

Guide on how to create a custom response using class-validator in NestJS

Answer №1

Answer №2

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