Customize error message in Nest js using class-validator

Question

I am working on a nest project, and using class-validator for validation.

Currently if there is any validation error, I am getting error response as

{
    "statusCode": 400,
    "message": [
        "Title is too long. Maximal length is 50 characters, but actual is $value",
        "Title is too short. Minimal length is 10 characters, but actual is $value"
    ],
    "error": "Bad Request"
}

But instead of message as array of string, can we have message as array of object. So, that FE can easy figure out which field is having the error, like

{
    "message": [
        { "field": "title", "error": "Title is too long. Maximal length is 50 characters, but actual is $value" },
        { "field": "title", "error": "Title is too short. Minimal length is 10 characters, but actual is $value" }
    ]
}

Answer 1

You can use exception filters in NestJS to handle or add custom user-friendly responses.

However, for the class-validator, there is the same mechanism by using exceptionFactory() in your validationPipe to modify the error returned by the class-validator, here is an example code for it:

app.useGlobalPipes(
  new ValidationPipe({
    exceptionFactory: (validationErrors: ValidationError[] = []) => {
      return new BadRequestException(
        validationErrors.map((error) => ({
          field: error.property,
          error: Object.values(error.constraints).join(', '),
        })),
      );
    },
  }),
);

Hope it will works for you!