Реализация CompareTo в качестве атрибута валидации

CompareToAttribute

using System;
using System.ComponentModel.DataAnnotations;

namespace ComponentModel.DataAnnotations
{
    /// <summary>
    /// Реализация CompareTo в качестве атрибута валидации.
    /// </summary>
    public class CompareToAttribute : ValidationAttribute
    {        
        public CompareToAttribute(string otherProperty, Comparison comparison)
        {
            _otherProperty = otherProperty;
            _comparison = comparison;
        }
        
        public override bool RequiresValidationContext => true;

        protected override ValidationResult IsValid(object value, ValidationContext validationContext)
        {
            var errorMessage = $"Unknown property: { _otherProperty}";
            var propertyInfo = validationContext.ObjectType.GetProperty(_otherProperty);

            if (propertyInfo != null)
            {
                var otherValue = propertyInfo.GetValue(validationContext.ObjectInstance, null);

                Comparison comparison;
                if (value != null)
                {
                    var diff = ((IComparable)value).CompareTo(otherValue);

                    if (diff < 0) comparison = Comparison.Less;
                    else if (diff == 0) comparison = Comparison.Equal;
                    else comparison = Comparison.Greater; 
                }
                else
                {
                    comparison = otherValue == null ? Comparison.Equal : Comparison.Less;
                }

                if ((_comparison & comparison) == comparison) return null;

                errorMessage = ErrorMessage;
            }

            return new ValidationResult(errorMessage);              
        }
               
        private readonly string _otherProperty;
        private readonly Comparison _comparison;
    }

    [Flags]
    public enum Comparison
    {
        Less = 1, Equal = 2, Greater = 4,
        NotEqual = Less | Greater,
        LessOrEqual = Less | Equal,
        GreaterOrEqual = Greater | Equal
    };
}