Linq - 序列包含多个元素

Question

我正在创建包含多个发票项目的发票。这是发票在多个发票项目中的显示方式：

当我刷新整个页面时，它会中断并抛出此错误：

 Sequence contains more than one element

这是我的代码：

   public ActionResult Create(long userId, long invoiceId)
    {
        ViewBag.InvoiceId = invoiceId;
        ViewBag.UserId = userId;
        ViewBag.UserId = userId;
        var objInvoiceItems = (from i in db.tblinvoiceitems
                      where i.InvoiceId == invoiceId
                      select i
                 ).ToList();

        var a = (from o in objInvoiceItems
                 select new InvoiceItemViewModel {
                     Description = o.DESCRIPTION,
                      Quantity = o.Quantity,
                       Rate = o.Rate,
                       Id = o.ID,
                       InvoiceId = o.InvoiceId
                 }).ToList();

        var objInvoice = (from i in db.tblinvoices
                          where i.ID == invoiceId
                          select i
                 ).ToList();

        var obj = (from i in objInvoice
                   join j in a
                   on i.ID equals j.InvoiceId
                   select new InvoiceCreateViewModel
                   {
                       AmountPaid = i.AmountPaid,
                       DueDate = i.DueDate,
                       InvoiceNo = i.ID,
                       UserId = i.UserId,
                       InvoiceItems = a
                       //InvoiceItems = j
                   }).SingleOrDefault();
        //obj.InvoiceItems = ListInvoiceItems(invoiceId.ToString()).Model;
        if (obj == null)
        {
            obj = new InvoiceCreateViewModel();
        }
        return View(obj);
    }


   public class InvoiceCreateViewModel
{
    public long? UserId { get; set; }
    public double? AmountPaid { get; set; }
    public DateTime? DueDate { get; set; }

    public double? TotalAmount { get; set; }
    public long InvoiceNo { get; set; }
    public double? Rate { get; set; }
    public string Description { get; set; }
    public int? Quantity { get; set; }

    public IEnumerable<InvoiceItemViewModel> InvoiceItems { get; set; }

}

它突破了SingleOrDefault()行。发票总是一个，InvoiceItems可以是多个。我通过jquery在一个不同的函数中处理Add new Invoice Items所以这个函数只在创建没有发票项目的新发票时被点击一次。

我想退回一张包含多个发票项目的发票;

Answer 1

如果你想将类组合成一个可以使用Razor引擎调用的模型，那么在视图的顶部声明一个viewModel就像这样

@model ViewModelExample

只需创建一个包含发票和发票项目列表的新模型

public class ViewModelExample
{
   public Invoice invoice{get; set;}
   public List<InvoiceItems> itemsList{get; set;}
}

为数据类型ViewModelExample分配正确的对象，如此

modelExample.invoice = obj
modelExample.itemsList= objInvoice

然后返回modelExample对象并使用Razer显示ViewModelExample类

中提供的每个属性的结果

Answer 2

您可以立即执行所有Linq查询（减少开销）

   var obj = (from invoice in db.tblinvoices
              where invoice.ID == invoiceId
              join items in db.tblinvoiceitems
              on invoice.ID == items.InvoiceId
              select new InvoiceCreateViewModel
                   {
                       AmountPaid = invoice.AmountPaid,
                       DueDate = invoice.DueDate,
                       InvoiceNo = invoice.ID,
                       UserId = invoice.UserId,
                       InvoiceItems = new List<InvoiceItemViewModel> {
                           Description = items.DESCRIPTION,
                           Quantity = items.Quantity,
                           Rate = items.Rate,
                           Id = items.ID,
                           InvoiceId = items.InvoiceId
                       }
                   }
              ).SingleOrDefault();