Asp.NetMVC数据注释自定义属性不起作用

我需要实现一个cusotm属性，然后使用asp.net数据注释来验证一个类。遗憾的是，在运行时没有调用属性类。请帮帮我。非常感谢。下面是源代码。

using System;
using System.Collections.Generic;
using CaseMgr.Model.Base;
using System.Linq;
using System.ComponentModel.DataAnnotations;
namespace CaseMgr.Model.BusinessObjects
{
    public partial class PatLiverException : BusinessBase<decimal>, IComparable<PatLiverException>, IEquatable<PatLiverException>
    {
        private LiverExcepDisease _liverExcepDisease = null;
        private DateTime _sccApprovalDate = new DateTime();
        public PatLiverException() { }
        public virtual LiverExcepDisease LiverExcepDisease
        {
            get { return _liverExcepDisease; }
            set { _liverExcepDisease = value; }
        }
        [SccApprovalDateValidate("SccApprovalDate", "LiverExcepDisease")]
        public virtual DateTime SccApprovalDate
        {
            get { return _sccApprovalDate; }
            set { _sccApprovalDate = value; }
        }
    }
    public class SccApprovalDateValidateAttribute : ValidationAttribute
    {
        public string m_SccApprovalDate { get; private set; }
        public string m_LiverExcepDisease { get; private set; }
        public SccApprovalDateValidateAttribute(string SccApprovalDate_PropertyName, string LiverExcepDisease_PropertyName)
        {
            this.m_SccApprovalDate = SccApprovalDate_PropertyName;
            this.m_LiverExcepDisease = LiverExcepDisease_PropertyName;
        }
        protected override ValidationResult IsValid(object value, ValidationContext context)
        {
            var SccApprovalDate_Property = context.ObjectType.GetProperty(m_SccApprovalDate);
            DateTime SccApprovalDate_Value = (DateTime)SccApprovalDate_Property.GetValue(context.ObjectInstance, null);
            var LiverExcepDisease_Property = context.ObjectType.GetProperty(m_LiverExcepDisease);
            LiverExcepDisease LiverExcepDisease_Value = (LiverExcepDisease)LiverExcepDisease_Property.GetValue(context.ObjectInstance, null);
            if (SccApprovalDate_Value != null && SccApprovalDate_Value != DateTime.MinValue && SccApprovalDate_Value != DateTime.MaxValue)
            {
                return LiverExcepDisease_Value.Id == 10 ? ValidationResult.Success : new ValidationResult("When other, SccApprovalDate can not be null.");
            }
            else
            {
                return ValidationResult.Success;
            }
        }
    }
}