C# 自定义Attribute

// 根据不同的region 设定name不同的最大长度和提示信息Region=APAC时，Name最长可以255，其他的Region最长时30

 public class QueryAddModels
    {
        [Required(ErrorMessage = "Please input Name")]        
        [RegularExpression(@"^([A-Za-z0-9_-]){1,300}$", ErrorMessage = "Only accept A-Z a-z 0-9 _ and -")]
        //[MaxLength(255, ErrorMessage = "The maximum allowable length is 255")]   
        [NameMaxLength] // 自定义
        public string Name
        {
            get; set;
        }

        [Required(ErrorMessage = "Please select Region")]
        public string Region
        {
            get; set;
        }
    
        [UserIDValidation] //自定义
        public string UserID { get; set; }

}

// NameMaxLength， Attribute 

 public class NameMaxLength : MaxLengthAttribute
    { 
        protected override ValidationResult IsValid(object value, ValidationContext validationContext)
        {
            var region = validationContext.ObjectType.GetProperty("Region")
                .GetValue(validationContext.ObjectInstance, null);

            var name = validationContext.ObjectType.GetProperty("Name")
                .GetValue(validationContext.ObjectInstance, null);

            if (region != null)
            {
                if (String.Equals(region.ToString(), "APAC") && name != null && name.ToString().Length>255)
                {
                    return new ValidationResult("The maximum allowable length is 255.");
                }
                else if (!String.Equals(region.ToString(), "APAC") && name != null && name.ToString().Length > 30)
                {
                    return new ValidationResult("The maximum allowable length is 30.");
                }
            }
            return ValidationResult.Success;
        }
    }

 public class UserIDValidation : ValidationAttribute
    {
        protected override ValidationResult IsValid(object value, ValidationContext validationContext)
        {
            var newUserID = validationContext.ObjectType.GetProperty("UserID")
                .GetValue(validationContext.ObjectInstance, null);

            if (newUserID !=null && !string.IsNullOrEmpty(newUserID .ToString()))
            {
                if (newUserID .ToString().ToUpper() != HttpContext.Current.Session["UserID "].ToString().ToUpper())
                    return new ValidationResult("UserID can'be changed");
                else
                    return ValidationResult.Success;
            }
            return new ValidationResult("UserID can't be empty");
        }

    }