FluentValidation modify error message in Must function

Question

Inside class that is responsible for validation I have simple rule:

RuleFor(u => u.Id)
    .Cascade(CascadeMode.StopOnFirstFailure)
    .NotEmpty().WithMessage("Id is required")
    .Must(ValidateId);

and below is my ValidateId function:

private bool ValidateId(CreateAccountBindingModel model, string id, PropertyValidatorContext context)
{
    if (id=="test")
    {
        context.Rule.CurrentValidator.ErrorCodeSource = new StaticStringSource("You are testing");
        return false;
    }

    var idValid = IdValidator.IsValid(id);
    if (!idValid)
    {
        context.Rule.CurrentValidator.ErrorCodeSource = new StaticStringSource("Id is invalid");
        return false;
    }
    return true;
}

If I run my validator I get default error, not my custom errors I'm specifying inside my function.
I've tried setting them using:

context.Rule.CurrentValidator.ErrorCodeSource = new StaticStringSource("Id is invalid");

but without any luck.

How can I define error message inside validation function?

Answer 1

You can use CustomValidator instead:

RuleFor(u => u.Id)
    .Cascade(CascadeMode.StopOnFirstFailure)
    .NotEmpty().WithMessage("Id is required")
    .Custom(ValidateId);

And below - ValidateId method:

private void ValidateId(string id, CustomContext context)
{
    if (id == "test")
    {
         context.AddFailure("You are testing");
    }
    var idValid = IdValidator.IsValid(id);
    if (!idValid)
    {
        context.AddFailure("Id is invalid");
    }
}