public void AddTaxService(int taxServiceId, int calculationMethod, decimal amount) { var t = TaxServices.SingleOrDefault(x => x.TaxServiceId == taxServiceId); if (t == null) { t = new TaxService { Amount = amount, CalculationType = calculationMethod, TaxServiceId = taxServiceId }; TaxServices.Add(t); } if (amount == 0) { if (t.Id > 0) { _removedTaxServices.Add(t); } TaxServices.Remove(t); } t.Amount = amount; }