gistfile1.cs

        [HttpPost]
        public ActionResult EditInvoice(Invoice invoice, string subaction)
        {
            ViewBag.Section = "Portfolio";
            ViewBag.Page = "Invoices";

            if (!string.IsNullOrEmpty(subaction))
            {
                ModelState.Clear();

                if (subaction == "add-item")
                {
                    invoice.Items.Add(new InvoiceItem() { Id = Guid.NewGuid(), InvoiceId = invoice.Id });
                }
                else if (subaction.StartsWith("delete-item"))
                {
                    var item = invoice.Items.Single(i => i.Id == Guid.Parse(subaction.Substring(12)));
                    invoice.Items.Remove(item);
                }
                PopulateClients();

                return View(invoice);
            }

            if (ModelState.IsValid)
            {
                db.Entry(invoice).State = EntityState.Modified;

                var dbvalues = db.Entry(invoice).GetDatabaseValues();

                var currentItems = db.InvoiceItems.Where(ii => ii.InvoiceId == invoice.Id).Select(ii => ii.Id).ToList();

                var deleted = currentItems.Where(i => !invoice.Items.Select(ii => ii.Id).Any(ii => ii == i));
                var added = invoice.Items.Where(i => !currentItems.Any(ii => ii == i.Id));
                //var modified = invoice.Items./*Except(deleted).*/Except(added);

                foreach (var item in invoice.Items)
                {
                    db.Entry(item).State = EntityState.Modified;
                }
                foreach (var item in deleted)
                {
                    db.InvoiceItems.Remove(db.InvoiceItems.Single(ii => ii.Id == item));
                }
                foreach (var item in added)
                {
                    db.Entry(item).State = EntityState.Added;
                }

                db.SaveChanges();

                return RedirectToAction("Invoices");
            }

            PopulateClients();

            return View(invoice);
        }