实体框架 - 在更新时保存子实体

我有一个发票实体，它有子发票日志实体。当我第一次创建发票并添加其 InvoiceLog 实体并保存时，它工作正常。但是，如果我随后编辑发票并尝试添加其他 InvoiceLog 实体，它会完全忽略新的 InvoiceLog 实体并且根本不保存它们。有什么想法我做错了吗？

//POST: /Secure/Invoices/Save/
        [AcceptVerbs(HttpVerbs.Post)]
        public ActionResult Save(Invoice invoice)
        {
            invoice.UpdateDate = DateTime.Now;
            invoice.DeveloperID = Developer.DeveloperID;
            invoice.InvoiceStatusID = (int)Enums.InvoiceStatus.Open;
            if (invoice.InvoiceID == 0)
            {//inserting new invoice.
                DataContext.InvoiceData.Insert(invoice);
            }
            else
            {//attaching existing invoice.
                DataContext.InvoiceData.Attach(invoice);
            }
            AddHours(invoice);
            //save changes.
            DataContext.SaveChanges();
            //redirect to invoice list.
            return RedirectToAction("Index");
        }

        private void AddHours(Invoice invoice)
        {
            //get existing logs.
            IQueryable<InvoiceLog> existingLogs = null;
            if(invoice.InvoiceID > 0)
            {
                existingLogs = DataContext.InvoiceData.GetLogs(invoice.InvoiceID);
            }
            //create new logs.
            var numDays = invoice.EndDate.Subtract(invoice.StartDate).TotalDays;
            for (int k = 0; k <= numDays; k++)
            {
                //check if log already exists.
                var existingLog = existingLogs.ToList().FindIndex(l => l.LogDate == invoice.StartDate.AddDays(k));
                if (existingLog == -1)
                {
                    //add new log.
                    var log = new InvoiceLog();
                    log.CreateDate = DateTime.Now;
                    log.UpdateDate = DateTime.Now;
                    log.Hours = 0;
                    log.InvoiceID = invoice.InvoiceID;
                    log.LogDate = invoice.StartDate.AddDays(k);
                    invoice.InvoiceLogs.Add(log);
                }
            }
        }

谢谢， 贾斯汀

您可以尝试添加InvoiceLogs附加之前的项目invoice:

    else
    {//attaching existing invoice.
        AddHours(invoice);
        DataContext.InvoiceData.Attach(invoice);
    }