public class YearCheck : ValidationAttribute
    {
        protected override ValidationResult IsValid(object value, ValidationContext validationContext)
        {
            Car car = (Car)validationContext.ObjectInstance;

            if (car == null)
                throw new ArgumentException("Atribute not applied on Car");

            if(car.Year > DateTime.Now.Year)
            {
                return new ValidationResult(GetErrorMessage(validationContext));
            }

            return ValidationResult.Success;
        }

        private string GetErrorMessage(ValidationContext validationContext)
        {
            if (!string.IsNullOrEmpty(this.ErrorMessage))
                return this.ErrorMessage;

            return "Can't Create car that has not been created yet";
        }
    }