Why can't I use resources as ErrorMessage with DataAnnotations?

Question

Why can\'t I do like this?

[Required(ErrorMessage = \"*\")]
[RegularExpression(\"^[a-zA-Z0-9_]*$\", ErrorMessage = Resources.RegistrationModel.UsernameError)         


        

Answer 1

When you are using the ErrorMessage property only constant strings or string literal can be assigned to it.

Use the ErrorMessageResourceType and ErrorMessageResourceName instead to specity your resources.

[RegularExpression(
    "^[a-zA-Z0-9_]*$", 
    ErrorMessageResourceType=typeof(Resources.RegistrationModel),
    ErrorMessageResourceName= "UsernameError"
)]

Note that the resources must be public (can be set in the resource editor).