C# 可为null的的企业库验证块

我正在玩企业库验证块。我在MVC项目中使用了一个从Linq到实体edmx文件的类。我希望确保可为空的DateTime始终晚于DateTime。我正在使用元数据类中的属性创建默认规则集。尝试使用PropertyComparisonValidator进行验证时，出现异常：

PropertyComparisonValidatorAttribute类型的验证属性不能用于验证值

我从理论上说，我无法将可空类型与结构进行比较，因此我专门编写了下面的自定义类，以解决这个问题。但我还是得到了这个例外：

类型为NullableDateComparisonValidatorAttribute的验证属性不能用于验证值

接下来，我尝试从企业库进行自我验证，但在验证时未能触发。在我弄明白这一点之前，我暂时处于停顿状态。请提出一个不太难看的解决方案\解决方法

using System;
using System.Reflection;
using Microsoft.Practices.EnterpriseLibrary.Validation;
using Microsoft.Practices.EnterpriseLibrary.Validation.Validators;

namespace IdahoUtility
{
    public class NullableComparisonValidator<T> : Validator<Nullable<T>>
        where T: struct, IComparable
    {
        protected string propertyToCompare { get; set; }
        protected ComparisonOperator comparisionOperator { get; set; }
        protected T TargetProperty(object currentTarget)
        {
            if (null == currentTarget)
            {
                throw new ArgumentNullException("currentTarget");
            }

            Type t = currentTarget.GetType();
            PropertyInfo pInfo = t.GetProperty(propertyToCompare);
            object oValue = pInfo.GetValue(currentTarget, null);

            if (oValue.GetType() != typeof(T))
            {
                throw new InvalidOperationException(string.Format("Property compared must be a {0}!",typeof(T)));
            }

            return (T)oValue;
        }
        public NullableComparisonValidator(string PropertyToCompare, ComparisonOperator cmpOp)
            :base(null,null)
        {
            if (string.IsNullOrWhiteSpace(PropertyToCompare))
            {
                throw new ArgumentException("PropertyToCompare is Invalid!", "PropertyToCompare");
            }
            propertyToCompare = PropertyToCompare;
            comparisionOperator = cmpOp;
        }
        protected override void DoValidate(Nullable<T> objectToValidate, object currentTarget, string key, ValidationResults validationResults)
        {
            // ignore nulls
            if (null == objectToValidate)
            {
                return;
            }

            switch (comparisionOperator)
            {
                case ComparisonOperator.Equal:
                    DoValidateEqual(objectToValidate, currentTarget, key, validationResults);
                    break;
                case ComparisonOperator.GreaterThan:
                    DoValidateGreaterThan(objectToValidate, currentTarget, key, validationResults);
                    break;
                case ComparisonOperator.GreaterThanEqual:
                    DoValidateGreaterThanEqual(objectToValidate, currentTarget, key, validationResults);
                    break;
                case ComparisonOperator.LessThan:
                    DoValidateLessThan(objectToValidate, currentTarget, key, validationResults);
                    break;
                case ComparisonOperator.LessThanEqual:
                    DoValidateLessThanEqual(objectToValidate, currentTarget, key, validationResults);
                    break;
                case ComparisonOperator.NotEqual:
                    DoValidateNotEqual(objectToValidate, currentTarget, key, validationResults);
                    break;             
            }
        }

        private void DoValidateLessThanEqual(Nullable<T> objectToValidate, object currentTarget, string key, ValidationResults validationResults)
        {
            if (objectToValidate.Value.CompareTo(TargetProperty(currentTarget)) > 0)
            {
                LogValidationResult(validationResults, string.Format("Should be less than or equal to {0}!", propertyToCompare), currentTarget, key);
            }
        }

        private void DoValidateLessThan(Nullable<T> objectToValidate, object currentTarget, string key, ValidationResults validationResults)
        {
            if (objectToValidate.Value.CompareTo(TargetProperty(currentTarget)) >= 0)
            {
                LogValidationResult(validationResults, string.Format("Should be less than {0}!", propertyToCompare), currentTarget, key);
            }
        }

        private void DoValidateGreaterThanEqual(Nullable<T> objectToValidate, object currentTarget, string key, ValidationResults validationResults)
        {
            if (objectToValidate.Value.CompareTo(TargetProperty(currentTarget)) < 0)
            {
                LogValidationResult(validationResults, string.Format("Should be greater than or equal {0}!", propertyToCompare), currentTarget, key);
            }
        }

        private void DoValidateGreaterThan(Nullable<T> objectToValidate, object currentTarget, string key, ValidationResults validationResults)
        {
            if (objectToValidate.Value.CompareTo(TargetProperty(currentTarget)) <= 0)
            {
                LogValidationResult(validationResults, string.Format("Should be greater than {0}!", propertyToCompare), currentTarget, key);
            }
        }

        private void DoValidateEqual(Nullable<T> objectToValidate, object currentTarget, string key, ValidationResults validationResults)
        {
            if (objectToValidate.Value.CompareTo(TargetProperty(currentTarget)) != 0)
            {
                LogValidationResult(validationResults, string.Format("Should be equal to {0}!", propertyToCompare), currentTarget, key);
            }
        }

        private void DoValidateNotEqual(Nullable<T> objectToValidate, object currentTarget, string key, ValidationResults validationResults)
        {
            if (objectToValidate.Value.CompareTo(TargetProperty(currentTarget)) == 0)
            {
                LogValidationResult(validationResults, string.Format("Should not be equal to {0}!", propertyToCompare), currentTarget, key);
            }
        }

        protected override string DefaultMessageTemplate
        {
            get { return "{0}"; }
        }
    }
}

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问题与它是可为null的类型无关。我最终彻底地重新进行了验证。我删除了带有属性的元数据类，并使用企业库工具将验证转移到配置。我终于能够使用属性比较验证器来确保结束日期跟在开始日期之后。最后一个障碍是我无法使用默认规则集。我在一个ASP.NETMVC网站中使用了它，并且我能够使用企业库进行客户端验证。事实上，我对整件事非常满意，即使我不清楚最初的设置为什么不起作用