FluentValidation: Check if one of two fields are empty

Question

I have this model

public class Person
{
    public int Id { get; set; }
    public string FirstName { get; set; }
    public string LastName         


        

Answer 1

I don't know that library, but if you just want to check those two properties for null, then you can use this:

RuleFor(person => person.FirstName ?? person.LastName).NotNull();

EDIT This doesn't work, because it throws an InvalidOperationException. Use Zabavsky's solution instead.