Question

Good day!

I’ve the following ViewModel class I use for login form:

using System.ComponentModel.DataAnnotations;

...

public class UserLogin : IDataErrorInfo
{           
    [Required]
    [DisplayName("Login")]
    public string Login { get; set; }

    [Required]
    [DisplayName("Password")]
    public string Password { get; set; }

    [DisplayName("Remember Me")]
    public bool RememberMe { get; set; }

    #region IDataErrorInfo Members

    // This will be a Model-level error
    public string Error
    {
        get
        {
            if (!WebUser.CanLogin(Login, Password))
            {
                return Resources.ValidationErrors.InvalidLoginPassword;
            }
            else
            {
                return String.Empty;
            }
        }
    }

    // All is handled by DataAnnotation attributes, just a stub for interface
    public string this[string columnName]
    {
        get
        {
            return string.Empty;
        }
    }
    #endregion

}

And this in Global.asax:

DefaultModelBinder.ResourceClassKey = "BinderMessages";
ValidationExtensions.ResourceClassKey = "BinderMessages";

The resource file BinderMessages.resx is placed inside App_GlobalResources it has two keys InvalidPropertyValue (which works) and PropertyValueRequired which doesn’t and gives me default message.

Question: Is it possible to modify this message, or it’s tied to DataAnnotations?

I’ve found many posts about this, but without solution. For now I just fallback to this:

[Required(ErrorMessageResourceType = typeof(Resources.ValidationErrors), ErrorMessageResourceName = "Required")] 

Answer 1

You can create a custom ValidationAttribute that extends RequiredAttribute and sets the values there. Something like:

public class MyRequiredAttribute : RequiredAttribute
{
    public MyRequiredAttribute()
    {
         ErrorMessageResourceType = typeof(Resources.ValidationErrors);
         ErrorMessageResourceName = "Required";
    }
}

Then decorate your Model with your custom attribute.

The default message is compiled into the DataAnnotations assembly in the resource file under System.ComponentModel.DataAnnotations.Resources.DataAnnotationsResources.resources and is RequiredAttribute_ValidationError=The {0} field is required.. So to answer your question, yes, that message is part of DataAnnotations.

Edit: PropertyValueRequired is used for errors on null values with non-nullable types. As mentioned below PropertyValueInvalid is used for type conversion errors.