How can I use a resource file for the message text within an EntLib attribute?

Question

I'm validating my business object properties using EntLib's validation attributes. I would like to localize the MessageTemplate text using a resource file, but I get the following compile time message when I do something like MessageTemplate = Resource.MyMessage:

"An attribute argument must be a constant expression, typeof expression or array creation expression of an attribute parameter type"

Is there a way to use a resource file for this text?

Thanks, Jay

Answer 1

You need to use the MessageTemplateResourceName and MessageTemplateResourceType properties instead of the MessageTemplate property.

Your code would look something like this:

[StringLengthValidator(1, 50, 
   MessageTemplateResourceName="InvalidLength", 
   MessageTemplateResourceType=typeof(MyResource))]
public string FirstName
{
    get;
    set;
}

Note that you can't use the the strongly typed resource class in the attribute (e.g. MyResource.InvalidLength) because the attribute is expecting a constant and the auto-generated class contains a property. (That is the reason for your error message.)

See Using the Message Template Resources for more information.