How to tell FluentValidation not to check rules for subfields of fields not included in the request?

Question

I am using FluentValidation version 9.2.2. I am getting this following message:

System.NullReferenceException: 'Object reference not set to an instance of an object.'

Json:

{ "geographyInfo": { "CountryCode": "UK" } }

RuleFor(x => x.Request.GeographyInfo)
    .NotEmpty()
    .WithMessage("GeographyInfo missing. Expected: object of type GeoInfo.")
    .WithErrorCode("123")
    .WithName("geographyInfo");

RuleFor(x => x.Request.GeographyInfo.CountryCode)
    .NotEmpty()
    .WithMessage("Field geographyInfo.CountryCode is missing. Expected: 3 digit code")
    .WithErrorCode("13")
    .WithName("countryCode");

Problem is, if I send a json like this: Json:

{ }

(with no geo info), I am getting a NullReferenceException, while I expect the "GeographyInfo missing. Expected: object of type GeoInfo."

What happens is I think FluentValidation goes ahead and checks also the 2nd rule: on field x.Request.GeographyInfo.CountryCode, but we don't have x.Request.GeographyInfo in this case, so it doesn't make sense to further reference the CountryCode.

How do I tell FluentValidation not to check rules for subfields of fields he doesnt find? (not included in the request)

Answer 1

For your particular case you could instruct FluentAPI to skip execution on first failure:

ValidatorOptions.CascadeMode = CascadeMode.StopOnFirstFailure;

Alternatively, you could use When method to first check if object is null:

When(x => x.Request.GeographyInfo != null, () => {   
    RuleFor(x => x.Request.GeographyInfo.CountryCode)
      .NotEmpty()
      .WithMessage("Field geographyInfo.CountryCode is missing. Expected: 3 digit code")
      .WithErrorCode("13")
      .WithName("countryCode");
});