Validating double? and string with GreaterThan

[blahetal]

Hi,
I am using your library in one of my projects for user input validations but I am not sure how to handle two cases

1 - validating a ViewModel which has two double? properties and one of them has to be greater than the other one (for two double's I can use GreateThan which works flawlesly but I am not sure how to use it for nullables)

2 - same as above but I have two strings which contain a double value and one of them should be greater than the other one. I tried to use builder.TransformToDouble(string) but I did not manage to compare it with the other string

Is it possible to compare such data types?

Thanks,
Libor

[Karnah]

Hi! It's looks like I didn't predict all possible cases. I can offer a quick solution for now, and I'll try to create a better solution in the future.

1. Please, create extensions method with such code:

        public static TNext GreaterThan<TObject, TProp, TNext>(
            this IRuleBuilderInitial<TObject, TProp?, TNext> ruleBuilder,
            Expression<Func<TObject, TProp?>> valueToCompareExpression,
            IComparer? comparer = null,
            ValidationMessageType validationMessageType = ValidationMessageType.Error)
            where TNext : IRuleBuilder<TObject, TProp?, TNext>
            where TObject : IValidatableObject
            where TProp : struct, IComparable<TProp>
        {
            return ruleBuilder.SetValidator(new GreaterThanValidator<TObject, TProp?, TProp?> (valueToCompareExpression, comparer, validationMessageType));
        }

Behavior: valid if any of values is null. Comparison result if both are not null.

        public static TNext GreaterThan<TObject, TNext>(
            this IRuleBuilderInitial<TObject, decimal?, TNext> ruleBuilder,
            Expression<Func<TObject, string>> valueToCompareExpression,
            ValidationMessageType validationMessageType = ValidationMessageType.Error)
            where TNext : IRuleBuilder<TObject, decimal?, TNext>
            where TObject : IValidatableObject
        {
            return ruleBuilder.SetValidator(new GreaterThanValidator<TObject, decimal?, string> (valueToCompareExpression, new DecimalStringComparer(), validationMessageType));
        }

        private class DecimalStringComparer : IComparer
        {
            /// <inheritdoc />
            public int Compare(object x, object y)
            {
                var left = (decimal?)x;
                var isRightDecimal = decimal.TryParse((string)y, out var right);
                var comparer = Comparer<decimal?>.Default;

                return isRightDecimal
                    ? comparer.Compare(left, right)
                    : comparer.Compare(left, null);
            }
        }

Behavior: valid if any of values is null. Also valid if string is not valid decimal number. Comparison result if both are not null and string is valid decimal.

[blahetal]

thank you for a prompt reply, I will test it