来自数据库的数据不能显示在 ASP.NET MVC 的下拉列表中

Question

我正在开发一个 ASP.NET MVC 项目。我正在尝试在添加和编辑页面上添加主详细信息。但是当我想编辑一条记录时，“纱线下拉列表”为空，但是当我调试项目数据时，项目数据正确来自数据库。我没有弄清楚这个问题。 Yarn 和 Yarn Detail 表之间的一对多关系，以及

//编辑页面

<table>
   <tr>
      <th>Yarn Name</th>
      <th>Unit Price of Yarn</th>
      <th>Percentage of Using</th>
      <th></th>
   </tr>
      @{ int i = 0;}
      @foreach (var x in Model.YarnDetails)
      {
                      
         <tr>
            <td>
               @Html.DropDownListFor(model => x.YarnID  , ViewBag.YarnList as SelectList, "--select--", new { @class = "form-control", @Name = "[" + i + "].YarnID" })
            </td>
                           
             <td>
                @Html.HiddenFor(model => x.YarnDetailID, new { @Name = "[" + i + "].YarnDetailID" })
                <input type="button" value="Remove" class="remove" />
             </td>
          </tr>
          i++;
      }
</table>

//控制器部分

public ActionResult Edit(int FabricCostCalcID)
    {

        var fabCo = _context.FabricCostCalcs.SingleOrDefault(c => c.FabricCostCalcID == FabricCostCalcID && c.IsDeleted == false);


        List<Fabric> fabriclist = _context.Fabrics.Where(x => x.IsDeleted == false).OrderBy(y => y.FabricName).ToList();
        List<KnittingOption> knittinglist = _context.KnittingOptions.Where(x => x.IsDeleted == false).OrderBy(y => y.KnittingName).ToList();
        List<Yarn> yarnList = _context.Yarns.Where(x => x.IsDeleted == false).OrderBy(y => y.YarnName).ToList();

        ViewBag.YarnList = new SelectList(yarnList, "YarnID", "YarnName");
        ViewBag.FabricList = new SelectList(fabriclist, "FabricID", "FabricName");
        ViewBag.KnitingList = new SelectList(knittinglist, "KnittingOptionID", "KnittingName");

        return PartialView("_EditPartial", fabCo);
    }

 [HttpPost]
public ActionResult Edit(FabricCostCalc fabricCost, List<YarnDetail> yarnDetails) 
    {

 
        _context.Entry(fabricCost).State = EntityState.Modified;

        foreach (var yar in yarnDetails)
        {

            yar.FabricCostCalcID = fabricCost.FabricCostCalcID;
           
            _context.Entry(yar).State = EntityState.Modified;
        }
        _context.SaveChanges();

        return RedirectToAction("Index");
    }

//前端屏幕截图

//DATABESE

提前谢谢你

Answer 1

我明白你想要做什么。如果你这样做会更好：

@for (int i = 0; i < Model.LSubCategories.Count(); i++)
{
                       <div class="col">
                            <label asp-for="SubCategory.CategoryID">Bulunacağı Kategori ?</label>
                              <div class="col">
                        <label asp-for="@Model.LSubCategories[i].CategoryID">Kategorisini seçiniz ?</label>
                        <select asp-for="@Model.LSubCategories[i].CategoryID" class="selectpicker" data-width="100%" name="CategoryID" required>
                            <option value="">Seçiniz</option>
                            @foreach (var item in Model.LSubCategories)
                            {
                                <option value="@item.CategoryID">@item.CategoryName</option>
                            }
                        </select>
}

我希望你能理解我的代码。 如果你意识到我在不使用 @Html.DropDownListFor 的情况下做同样的事情。 如果你想调用相关数据，你可以在你的 ViewModel 中定义它。之后，您可以将其填写在您的控制器中：

 var list = _unitOfWorkSCat.RepositorySubCategory.GetAll();
            var listCat = _unitOfWorkCat.RepositoryCategory.GetAll();
            var listL = _unitOfWorkSCat.RepositorySubCategory.GetAllAsList();
            var SubCategory = new SubCategory();
            var CategoryViewModel = new CategoryViewModel
            {
                SubCategories = list,
                SubCategory = SubCategory,
                LSubCategories = listL,
                Categories = listCat
            };