public string StartPage { get; set; }
public Guid CustomTargetGuid {get;set;}
public class EntityValidator : AbstractValidator<Entity>
RuleFor(p => p.CustomTargetGuid)
.When(p => p.StartPage == "10F5F529-4858-448E-8B62-1478DAB7232A");
public static void Main()
var entityValidator = new EntityValidator();
var check = new Entity(){
StartPage = "10F5F529-4858-448E-8B62-1478DAB7232A",
CustomTargetGuid = Guid.Empty
var result = entityValidator.Validate(check);
Console.WriteLine(result.IsValid);
foreach (var error in result.Errors)
Console.WriteLine(" Error: " + error.ErrorMessage);