Get min constraints from class-validator in nestjs ValidationPipe exceptionFactory

Question

I want to create a nestjs app and want to have the ability to customize the messages of class-validator, so I created a function to get keys I provide to messages and then returns the customized message, the problem is I want to get min value I provide to @Min decorator in DTOs; but it does not exist in error object I get in exceptionFactory.

this Is the DTO:

class GetUsersDto {
  @ApiProperty({ required: false })
  @IsOptional()
  @Min(1, { message: 'validation.min' })
  @IsInt()
  @Transform((param) => parseInt(param.value, 10))
  page?: number;
}

  app.useGlobalPipes(
    new ValidationPipe({
      stopAtFirstError: true,
      whitelist: true,
      forbidNonWhitelisted: true,
      transform: true,
      exceptionFactory: (errors) => {
        console.log(errors);
        const result = errors
          .map((error) => {
            const key = Object.values(error.constraints)[0];
            const message = getMessage(key, error);
            return message ? message : getMessage('validation.400');
          })
          .join('');
        return new BadRequestException(result);
      },
    }),
  );

When I log errors inside exceptionFactory I get something like this:

[
  ValidationError {
    target: GetUsersDto { page: -1 },
    value: -1,
    property: 'page',
    children: [],
    constraints: { min: 'validation.min' }
  }
]

what I need is to get the minimum value I provided to @Min (which is 1 here), but I get validation.min. How can I get the value provided to @Min?.

we can use context, but providing the same value in two places is error prone and adding context is making decorators a little bit messy.

Answer 1

You can use a global const for that value. like this:

const MIN_PAGE = 1

class GetUsersDto {
   @ApiProperty({ required: false })
   @IsOptional()
   @Min(MIN_PAGE , { message: 'the min value page is:' + MIN_PAGE })
   @IsInt()
   @Transform((param) => parseInt(param.value, 10))
   page?: number;
}

and then you will be able to use that const wherever you want. Yo can even use a separated constans.js file and store all the config values there and import them wherever you need.