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

在Asp.Net MVC中实现CompareValues标签对Model中的属性进行验证2014-08-27 博客园 Eric Sun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 propertyvar property = validationContext.ObjectType.GetProperty（OtherProperty）;// check it is not nullif （property == null）return new ValidationResult（String.Format（"Unknown property: {0}.", OtherProperty））;// check typesvar 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 valuevar 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 IComparablesif （！（value is IComparable） || ！（other is IComparable））return new ValidationResult（String.Format（"{0} and {1} must both implement IComparable", validationContext.DisplayName, OtherProperty））;// compare the objectsvar result = Comparer.Default.Compare（value, other）;switch （Criteria）{case CompareValues.GreaterThan:if （result > 0）return null;break;case CompareValues.LessThan:if （result < 0）return null;break;case CompareValues.GreatThanOrEqualTo:if （result >= 0）return null;break;case CompareValues.LessThanOrEqualTo:if （result <= 0）return null;break;}}// got this far must mean the items don"t meet the comparison criteriareturn 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