[C#] Adding annotations/metadata with partial classes

HappyfunBallMetadata.cs

    [MetadataType(typeof(HappyFunBallMetadata))]
    public partial class HappyFunBall
    {
        public int      Id { get; set; }

        public string   Name { get; set; }
        public Color    Colour { get; set; }
        public int      Weight { get; set; }

    }

    public partial class HappyFunBall
    {
        public class HappyFunBallMetadata
        {

            [Required(ErrorMessageResourceType = typeof(Resources), ErrorMessageResourceName = "HappyFunBallIdRequired")]
            public int Id { get; set; }

            [StringLength(25)]
            [Required(ErrorMessageResourceType = typeof(Resources), ErrorMessageResourceName = "HappyFunBallNameRequired")]
            public string Name { get; set; }

            public Color Colour { get; set; }

            public int Weight { get; set; }

        }
    }

        static List<ValidationResult> Validate(object instance, Type metaDataType)
        {
            return Validate(instance, metaDataType, true);
        }

        static List<ValidationResult> Validate(object instance, Type metaDataType, bool validateAllObjects)
        {
            var listOfErrors = new List<ValidationResult>();

            var T = instance.GetType();

            // Spider through the object's attributes to determine if the MetadataTypeAttribute is provided
            //$$$$BUG:BUG var metaDataType = T.GetCustomAttributes(typeof(MetadataTypeAttribute), true).First() as Type;

            //TypeDescriptor.AddProviderTransparent(
            //    new AssociatedMetadataTypeTypeDescriptionProvider(T,
            //        typeof(HappyFunBall.HappyFunBallMetadata)), T);

            TypeDescriptor.AddProviderTransparent(
                new AssociatedMetadataTypeTypeDescriptionProvider(T, metaDataType), T);

            var validationContext = new ValidationContext(instance, null, null);
            //var listOfErrors = new List<ValidationResult>();

            var isValid = Validator.TryValidateObject(instance, validationContext, listOfErrors, true);

            if (!isValid)
            {
                StringBuilder errorMsg = new StringBuilder();
                listOfErrors.ForEach((ValidationResult ex) =>
                    errorMsg.Append(ex.ErrorMessage)
                    );
                throw new ValidationException(errorMsg.ToString());
            }

            return listOfErrors;
        }

        static void Main(string[] args)
        {

            try
            {

                var myBall = new HappyFunBall();

                var validationResults = Validate(myBall, typeof(HappyFunBall.HappyFunBallMetadata));
                if (validationResults != null)
                {
                    validationResults.ForEach(result =>
                    {
                        Console.WriteLine(result.ErrorMessage);
                    });
                }

                Console.ForegroundColor = ConsoleColor.Green;
                Console.WriteLine("All is well!");
            }
            catch (Exception ex)
            {
                Console.ForegroundColor = ConsoleColor.Red;
                Console.WriteLine(ex.Message);

            }
            finally
            {
                Console.ResetColor();
            }

            Console.WriteLine("Press any key to quit...");
            Console.ReadKey();
        }