Created
March 24, 2015 13:06
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Compare values attribute
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/// <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> | |
[AttributeUsageAttribute(AttributeTargets.Property | AttributeTargets.Field | AttributeTargets.Parameter, AllowMultiple = false)] | |
public class CompareAttribute : 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 CompareAttribute(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 | |
if (validationContext.ObjectType.GetProperty(validationContext.MemberName).PropertyType != property.PropertyType) | |
return new ValidationResult(String.Format("The types of {0} and {1} must be the same.", validationContext.DisplayName, 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 > 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 criteria | |
return new ValidationResult(FormatErrorMessage(validationContext.DisplayName)); | |
} | |
/// <summary> | |
/// Applies formatting to an error message. | |
/// </summary> | |
/// <param name="name">The name to include in the error message</param> | |
/// <returns></returns> | |
public override string FormatErrorMessage(string name) | |
{ | |
return String.Format(CultureInfo.CurrentCulture, base.ErrorMessageString, name, OtherProperty, Criteria.Description()); | |
} | |
/// <summary> | |
/// retrieve the object to compare to | |
/// </summary> | |
/// <returns></returns> | |
object GetOther(ValidationContext context) | |
{ | |
return null; | |
} | |
} | |
/// <summary> | |
/// Indicates a comparison criteria used by the CompareValues attribute | |
/// </summary> | |
public enum CompareValues | |
{ | |
[Description("equal to")] | |
EqualTo, | |
[Description("not equal to")] | |
NotEqualTo, | |
[Description("greater than")] | |
GreaterThan, | |
[Description("less than")] | |
LessThan, | |
[Description("greater than or equal to")] | |
GreatThanOrEqualTo, | |
[Description("less than or equal to")] | |
LessThanOrEqualTo | |
} | |
/// <summary> | |
/// Extension methods for enums | |
/// </summary> | |
public static class EnumExtensions | |
{ | |
/// <summary> | |
/// Get the description attribute for the enum | |
/// </summary> | |
/// <param name="e"></param> | |
/// <returns></returns> | |
public static string Description(this Enum e) | |
{ | |
var da = (DescriptionAttribute[])(e.GetType().GetField(e.ToString()).GetCustomAttributes(typeof(DescriptionAttribute), false)); | |
return da.Length > 0 ? da[0].Description : e.ToString(); | |
} | |
} |
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