Throw same error format as `class-validator` in NestJS

Question

Let's have this controller in NestJS project:

  @Post('resetpassword')
  @HttpCode(200)
  async requestPasswordReset(
    @Body() body: RequestPasswordResetDTO,
  ): Promise<boolean> {
    try {
      return await this.authService.requestPasswordReset(body);
    } catch (e) {
      if (e instanceof EntityNotFoundError) {
        // Throw same exception format as class-validator throwing (ValidationError)
      } else throw e;
    }
  }

Dto definition:

export class RequestPasswordResetDTO {
  @IsNotEmpty()
  @IsEmail()
  public email!: string;
}

I want to throw error in ValidationError format (property, value, constraints, etc) when this.authService.requestPasswordReset(body); throws an EntityNotFoundError exception.

How I can create this error manually? Those errors are just thrown when DTO validation by class-validator fails. And those can be just static validations, not async database validations.

So the final API response format should be for example:

{
    "statusCode": 400,
    "error": "Bad Request",
    "message": [
        {
            "target": {
                "email": "[email protected]"
            },
            "value": "[email protected]",
            "property": "email",
            "children": [],
            "constraints": {
                "exists": "email address does not exists"
            }
        }
    ]
}

I need it to have consistent error handling :)

Answer 1

When adding the ValidationPipe to your app, provide a custom exceptionFactory:

  app.useGlobalPipes(
    new ValidationPipe({
      exceptionFactory: (validationErrors: ValidationError[] = []) => {
        return new BadRequestException(validationErrors);
      },
    })
  );

This should be all you need to get the intended result.

For comparison, you can check out the original NestJS version here.

Answer 2

You could use an Exception Filter to create your customized response to that exception First we define the Exception Filter:

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

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

    response
      .status(status)
      .json({
        "statusCode": 400,
        "error": "Bad Request",
        "message": [
          {
            "target": {},
            "property": "email",
            "children": [],
            "constraints": {
              "isEmail": "email must be an email"
            }
          },
          // other field exceptions
        ]
      });
  }
}

Then back in your controller, you use the filter:

  // ...
  import { EntityNotFoundExceptionFilter } from 'its module';
  // ...
  @Post('resetpassword')
  @HttpCode(200)
  @UseFilters(EntityNotFoundExceptionFilter)
  async requestPasswordReset(
    @Body() body: RequestPasswordResetDTO
  ): Promise<boolean> {
      return await this.authService.requestPasswordReset(body);
  }

This should work just fine.

Answer 3

We can get back the exception response thrown by class-validator and set to response,

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

@Catch()
export class ValidationFilter < T > implements ExceptionFilter {
  catch (exception: T, host: ArgumentsHost) {
    if (exception instanceof BadRequestException) {
      const response = host.switchToHttp().getResponse();
      response.status(exception.getStatus())
        .json(exception.getResponse());
    }
  }
}

Controller should look,

@Post('create')
@UsePipes(ValidationPipe)
@UseFilters(ValidationFilter)
async create(@Body() body: CreateDto) {

}