protected override ValidationResult IsValid(object value, ValidationContext validationContext) { CitySqlDAO citySqlDAO = new CitySqlDAO(@"Data Source=.\SQLEXPRESS;Initial Catalog=World;Integrated Security=True"); List <string> countryCodes = citySqlDAO.GetCountryCodes().ToList(); City city = (City)validationContext.ObjectInstance; if (!countryCodes.Contains(city.CountryCode)) { return(new ValidationResult("Country Code does not exist. Please try again.")); } return(ValidationResult.Success); }