private void Fixuptown_city(town_city previousValue) { if (previousValue != null && previousValue.addresses.Contains(this)) { previousValue.addresses.Remove(this); } if (town_city != null) { if (!town_city.addresses.Contains(this)) { town_city.addresses.Add(this); } if (town_city_id != town_city.id) { town_city_id = town_city.id; } } else if (!_settingFK) { town_city_id = null; } }