cannot convert method group to func<long,bool>

Question

I am trying to use fluentvalidation to validate pin to ensure what user type match with existing pin. AppDbContext is the context class which inherit from dbcontext (Entity Framework). I have this syntax error while calling isOldPin method. If PinCodeOld datatype is string, this error doesn't appear. But if PinCodeOld datatype is long, this error appear.

 public class ChangePinValidator : AbstractValidator<VMPinChange>
{
    private readonly AppDbContext db = new AppDbContext();
    public ChangePinValidator()
    {
        RuleFor(b => b.PinCodeOld).Must(isOldPin).WithMessage("Invalid current pin code.");
        RuleFor(b => b.PinCodeNew).Equal(b => b.PinCodeConfirmation)
            .WithMessage("New pin code is not same with confirmed new pin code.");
    }

    private bool isOldPin(string _currentPin)
    {
        bool isMatch = db.BankAccounts.Any(b => b.PinCode.Equals(_currentPin));

        return isMatch;
    }
}

Answer 1

The problem is this:

RuleFor(b => b.PinCodeOld).Must(isOldPin)

If PinCodeOld is a long, then the Must method is going to expect a method that takes a long value as input, but your method takes a string . If you need it to be long then you also need to change the isOldPin to take a long .