Custom validation attribute that compares the value of my property with another property's value in my model class

Question

I want to create a custom validation attribute, in which I want to compare the value of my property with another property's value in my model class. For example I have in my model class:

...     public string SourceCity { get; set; } public string DestinationCity { get; set; } 

And I want to create a custom attribute to use it like this:

[Custom("SourceCity", ErrorMessage = "the source and destination should not be equal")] public string DestinationCity { get; set; } //this wil lcompare SourceCity with DestinationCity 

How can I get there?

Answer 1

Here's how you could obtain the other property value:

public class CustomAttribute : ValidationAttribute {     private readonly string _other;     public CustomAttribute(string other)     {         _other = other;     }      protected override ValidationResult IsValid(object value, ValidationContext validationContext)     {         var property = validationContext.ObjectType.GetProperty(_other);         if (property == null)         {             return new ValidationResult(                 string.Format("Unknown property: {0}", _other)             );         }         var otherValue = property.GetValue(validationContext.ObjectInstance, null);          // at this stage you have "value" and "otherValue" pointing         // to the value of the property on which this attribute         // is applied and the value of the other property respectively         // => you could do some checks         if (!object.Equals(value, otherValue))         {             // here we are verifying whether the 2 values are equal             // but you could do any custom validation you like             return new ValidationResult(this.FormatErrorMessage(validationContext.DisplayName));         }         return null;     } }