在Asp.Net MVC中实现CompareValues标签对Model中的属性进行验证

在Asp.Net MVC中可以用继承ValidationAttribute的方式，自定制实现Model两个中两个属性值的比较验证

具体应用场景为：要对两个属性值的大小进行验证

代码如下所示：

    /// <summary>
    /// Specifies that the field must compare favourably with the named field, if objects to check are not of the same type
    /// false will be return
    /// </summary>
    public class CompareValuesAttribute : ValidationAttribute
    {
        /// <summary>
        /// The other property to compare to
        /// </summary>
        public string OtherProperty { get; set; }

        public CompareValues Criteria { get; set; }

        /// <summary>
        /// Creates the attribute
        /// </summary>
        /// <param name="otherProperty">The other property to compare to</param>
        public CompareValuesAttribute(string otherProperty, CompareValues criteria)
        {
            if (otherProperty == null)
                throw new ArgumentNullException("otherProperty");

            OtherProperty = otherProperty;
            Criteria = criteria;
        }

        /// <summary>
        /// Determines whether the specified value of the object is valid.  For this to be the case, the objects must be of the same type
        /// and satisfy the comparison criteria. Null values will return false in all cases except when both
        /// objects are null.  The objects will need to implement IComparable for the GreaterThan,LessThan,GreatThanOrEqualTo and LessThanOrEqualTo instances
        /// </summary>
        /// <param name="value">The value of the object to validate</param>
        /// <param name="validationContext">The validation context</param>
        /// <returns>A validation result if the object is invalid, null if the object is valid</returns>
        protected override ValidationResult IsValid(object value, ValidationContext validationContext)
        {
            // the the other property
            var property = validationContext.ObjectType.GetProperty(OtherProperty);

            // check it is not null
            if (property == null)
                return new ValidationResult(String.Format("Unknown property: {0}.", OtherProperty));

            // check types
            var memberName = validationContext.ObjectType.GetProperties().Where(p => p.GetCustomAttributes(false).OfType<DisplayAttribute>().Any(a => a.Name == validationContext.DisplayName)).Select(p => p.Name).FirstOrDefault();
            if (memberName == null)
            {
                memberName = validationContext.DisplayName;
            }
            if (validationContext.ObjectType.GetProperty(memberName).PropertyType != property.PropertyType)
                return new ValidationResult(String.Format("The types of {0} and {1} must be the same.", memberName, OtherProperty));

            // get the other value
            var other = property.GetValue(validationContext.ObjectInstance, null);

            // equals to comparison,
            if (Criteria == CompareValues.EqualTo)
            {
                if (Object.Equals(value, other))
                    return null;
            }
            else if (Criteria == CompareValues.NotEqualTo)
            {
                if (!Object.Equals(value, other))
                    return null;
            }
            else
            {
                // check that both objects are IComparables
                if (!(value is IComparable) || !(other is IComparable))
                    return new ValidationResult(String.Format("{0} and {1} must both implement IComparable", validationContext.DisplayName, OtherProperty));

                // compare the objects
                var result = Comparer.Default.Compare(value, other);

                switch (Criteria)
                {
                    case CompareValues.GreaterThan:
                        if (result > )
                            return null;
                        break;
                    case CompareValues.LessThan:
                        if (result < )
                            return null;
                        break;
                    case CompareValues.GreatThanOrEqualTo:
                        if (result >= )
                            return null;
                        break;
                    case CompareValues.LessThanOrEqualTo:
                        if (result <= )
                            return null;
                        break;
                }
            }

            // got this far must mean the items don't meet the comparison criteria
            return new ValidationResult(ErrorMessage);
        }
    }

    /// <summary>
    /// Indicates a comparison criteria used by the CompareValues attribute
    /// </summary>
    public enum CompareValues
    {
        EqualTo,
        NotEqualTo,
        GreaterThan,
        LessThan,
        GreatThanOrEqualTo,
        LessThanOrEqualTo
    }

应用的时候直接在指定的属性上添加此CompareValuesAttribute标签即可

【注：第一个参数是要与之比较的属性名，第二个参数表示两个属性值之间的大小关系，第三个参数表示错误提示信息】

public class EricSunModel
{
    [Display(Name = "Ready Time")]
    public string ReadyTime { get; set; }

    [CompareValues("ReadyTime", CompareValues.GreaterThan, ErrorMessage = "Close time must be later than ready time")]
    [Display(Name = "Close Time")]
    public string CloseTime { get; set; }

}

更多细节可以参考如下链接：

http://cncrrnt.com/blog/index.php/2011/01/custom-validationattribute-for-comparing-properties/

这里提供一个我自己的增强版本，可以添加另外一个依赖条件。

代码如下：

    public class CompareValuesAttribute : ValidationAttribute
    {
        /// <summary>
        /// The other property to compare to
        /// </summary>
        public string OtherProperty { get; set; }
        public CompareCriteria Criteria { get; set; }

        /// <summary>
        /// The other dependent rule
        /// </summary>
        public string RulePropertyName { get; set; }
        public CompareCriteria RuleCriteria { get; set; }
        public object RulePropertyValue { get; set; }

        public bool CustomErrorMessage { get; set; }

        /// <summary>
        /// Compare values with other property based on other rules or not
        /// </summary>
        /// <param name="otherProperty">other property.</param>
        /// <param name="criteria">criteria</param>
        /// <param name="rulePropertyName">rule property name. (if don't based on other rules, please input null)</param>
        /// <param name="ruleCriteria">rule criteria. (if don't based on other rules, please input null)</param>
        /// <param name="rulePropertyValue">rule property value. (if don't based on other rules, please input null)</param>
        /// <param name="customErrorMessage">custom error message. (if don't need customize error message format, please input null)</param>
        public CompareValuesAttribute(string otherProperty, CompareCriteria criteria, string rulePropertyName, CompareCriteria ruleCriteria, object rulePropertyValue, bool customErrorMessage)
        {
            OtherProperty = otherProperty;
            Criteria = criteria;
            RulePropertyName = rulePropertyName;
            RuleCriteria = ruleCriteria;
            RulePropertyValue = rulePropertyValue;
            CustomErrorMessage = customErrorMessage;
        }

        /// <summary>
        ///  Compare values with other property
        /// </summary>
        /// <param name="otherProperty"></param>
        /// <param name="criteria"></param>
        /// <param name="customErrorMessage"></param>
        public CompareValuesAttribute(string otherProperty, CompareCriteria criteria, bool customErrorMessage)
        {
            OtherProperty = otherProperty;
            Criteria = criteria;
            RulePropertyName = null;
            CustomErrorMessage = customErrorMessage;
        }

        protected override ValidationResult IsValid(object value, ValidationContext validationContext)
        {
            if (ValidateDependentRule(validationContext) == null)   //validate dependent rule successful
            {
                if (OtherProperty == null)
                {
                    return new ValidationResult(String.Format("Orther property is null."));
                }

                // the the other property
                var property = validationContext.ObjectType.GetProperty(OtherProperty);

                // check it is not null
                if (property == null)
                {
                    return new ValidationResult(String.Format("Unknown property: {0}.", OtherProperty));
                }

                // check types
                var memberName = validationContext.ObjectType.GetProperties().Where(p => p.GetCustomAttributes(false).OfType<DisplayAttribute>().Any(a => a.Name == validationContext.DisplayName)).Select(p => p.Name).FirstOrDefault();
                if (memberName == null)
                {
                    memberName = validationContext.DisplayName;
                }
                if (validationContext.ObjectType.GetProperty(memberName).PropertyType != property.PropertyType)
                {
                    return new ValidationResult(String.Format("The types of {0} and {1} must be the same.", memberName, OtherProperty));
                }

                // get the other value
                var other = property.GetValue(validationContext.ObjectInstance, null);

                if (CompareValues(value, other, Criteria, validationContext) == null)
                {
                    return null;
                }
                else
                {
                    // got this far must mean the items don't meet the comparison criteria
                    if (CustomErrorMessage)
                    {
                        return new ValidationResult(string.Format(ErrorMessage, other));
                    }
                    else
                    {
                        return new ValidationResult(ErrorMessage);
                    }
                }
            }
            else
            {
                return null;    //dependent rule isn't exist or validate dependent rule failed
            }
        }

        private ValidationResult ValidateDependentRule(ValidationContext validationContext)
        {
            ValidationResult validateRuleResult = null;

            // has dependent rule
            if (RulePropertyName != null)
            {
                var rulePropertyName = validationContext.ObjectType.GetProperty(RulePropertyName);
                if (rulePropertyName == null)
                    return new ValidationResult(String.Format("Unknown rule property name: {0}.", RulePropertyName));

                var rulePropertyRealValue = rulePropertyName.GetValue(validationContext.ObjectInstance, null);

                validateRuleResult = CompareValues(rulePropertyRealValue, RulePropertyValue, RuleCriteria, validationContext);
            }

            return validateRuleResult;
        }

        private ValidationResult CompareValues(object targetValue, object otherValue, CompareCriteria compareCriteria, ValidationContext validationContext)
        {
            ValidationResult compareResult = new ValidationResult("Compare Values Failed.");

            // equals to comparison,
            if (compareCriteria == CompareCriteria.EqualTo)
            {
                if (Object.Equals(targetValue, otherValue)) compareResult = null;
            }
            else if (compareCriteria == CompareCriteria.NotEqualTo)
            {
                if (!Object.Equals(targetValue, otherValue)) compareResult = null;
            }
            else
            {
                // check that both objects are IComparables
                if (!(targetValue is IComparable) || !(otherValue is IComparable))
                    compareResult = new ValidationResult(String.Format("{0} and {1} must both implement IComparable", validationContext.DisplayName, OtherProperty));

                // compare the objects
                var result = Comparer.Default.Compare(targetValue, otherValue);

                switch (compareCriteria)
                {
                    case CompareCriteria.GreaterThan:
                        if (result > ) compareResult = null;
                        break;
                    case CompareCriteria.LessThan:
                        if (result < ) compareResult = null;
                        break;
                    case CompareCriteria.GreatThanOrEqualTo:
                        if (result >= ) compareResult = null;
                        break;
                    case CompareCriteria.LessThanOrEqualTo:
                        if (result <= ) compareResult = null;
                        break;
                }
            }

            return compareResult;
        }
    }

    public enum CompareCriteria
    {
        EqualTo,
        NotEqualTo,
        GreaterThan,
        LessThan,
        GreatThanOrEqualTo,
        LessThanOrEqualTo
    }