public Manufacturer CreateManufacturer(Manufacturer manufacturer) { if (manufacturer.ManufacturerId < 0) { throw new ArgumentException("Manufacturer ID for new car can not be negative"); } if (_manuRepository.ReadManufacturerById(manufacturer.ManufacturerId) != null) { throw new InvalidOperationException("Manufacturer ID can not match car which already exists"); } if (_validator != null) { _validator.ValidateManufacturer(manufacturer); } return(_manuRepository.AddManufacturer(manufacturer)); }