Question

This is the problem that we’re facing in .NET MVC 2.

We’re trying to use DataAnnotations to take care of the Model Validation for us, like it’s supposed to. The only problem that we’re having is that we don’t want the standard error messages (because we have multiple languages on our website).

We want to localize this, but the way the site is setup, is that all text comes from a database. So we’d like to have our error messages in the database as well.

So we wrote a custom RequiredAttribute, like this:

public class LocalizedRequiredAttribute : RequiredAttribute
{   
    public string LocalizedErrorMessage
    {
        get
        {
            return ErrorMessage;
        }
        set
        {
            ErrorMessage = value.Translate();
        }
    }

}

We wrote an extension to the String class to add the “Translate()” method, which does the necessary database lookup for the correct localized version.

We use our attribute like this:

[LocalizedRequired(LocalizedErrorMessage = "Naam is required")]
public string Name {get; set; }

This works, but only once.

If you visit the site in French first, you’ll see the French error message stating that you’re supposed to enter a value. If you visit the English site later, you’ll still see the French error on the English page. The Setter seems to be called only once.

What can we do to prevent this behavior and refresh the error message every time the validation is run / the model is populated with values?

Thanks for any help you can give me.

Answer 1

Couldn’t you fix this by moving your .Translate() from your setter to your getter? It makes sense that your setter is called only once.

Edit:
I assumed ErrorMessage was a virtual message, which is not the case.

Your only option might be to create Resource class (you don’t need a resource file) that retrieves your values from the database.

[Required(ErrorMesageResourceName="FirstName", ErrorMessageResourceType=typeof(ABCResourceClass))]  
public string Name {get; set; } 

class ABCResourceClass{
  public static String  FirstName{
    get{
        return Translate("FirstName");
    }
  }

}

As you can infer from the example, the annotations framework calls the property with the name that matches the string you provide to ErrorMessageResourceName.

You could resort to some kindof code generation technique to create the ABCResourceClass if you have a lot of properties.