System.ComponentModel.DataAnnotations.compare vs System.Web.Mvc.Compare

Question

MVC 4 Beta project fails to compile after upgrading to .Net 4.5.

This happens due to conflict between System.ComponentModel.DataAnnotations.CompareAttribute and System.Web.Mvc.CompareAttribute

System.ComponentModel.DataAnnotations.CompareAttribute MSDN documentation says:

Provides an attribute that compares two properties.

While System.Web.Mvc.CompareAttribute MSDN documentation says:

Provides an attribute that compares two properties of a model.

What is the difference between the two and when it would be "smarter" to use each of them?

10x.

Answer 1

So, looking at the MSDN documentation and doing a literal comparison of the two classes, I noticed both classes are derived from System.ComponentModel.DataAnnotations.ValidationAttribute. In fact, the classes are almost exactly the same. The only notable difference is that the MVC version also implements IClientValidatable which adds the following properties:

• FormatPropertyForClientValidation - (static member) Formats the property for client validation by prepending an asterisk and a dot.
• GetClientValidationRules - Gets a list of compare-value client validation rules for the property using the specified model metadata and controller context.

As for which class you should use, if the model will be directly bound to a view, use the MVC version so that you can take advantage of the client-side validation. However, if you're using ViewModels, you can stick with the ComponentModel class and avoid the unnecessary overhead of the additional properties. Your call!

• System.Web.Mvc.CompareAttribute

• System.ComponentModel.DataAnnotations.CompareAttribute