单击创建新孔时，希望能够选择一个CourseId

如何解决单击创建新孔时，希望能够选择一个CourseId

我正在尝试创建一个高尔夫比分应用程序。我创建了具有以下表格“ Round”，“ Course”和“ Hole”的数据库。

孔表具有一个指向courseId的外键，就像在创建每个孔时一样，我希望将其链接到课程。

当单击“新建”时，我希望有一个下拉列表，用于在输入所有孔的详细信息时选择CourseId。

但是当我单击“新建”时，在“孔”视图模型中出现以下错误。

System.ArguementNullException：值不能为Null。参数名称项。在HoleviewmodelController内的“创建动作”代码中。

这是我的Holeviewmodel代码

    public class Holeviewmodel
{
    [Key]
    public int HoleId { get; set; }

    public int HoleNumber { get; set; }

    public int Par { get; set; }

    public int Length { get; set; }

    public int strokeIndex { get; set; }

    [ForeignKey("Course")]
    public int? CourseId { get; set; }
    public IEnumerable<SelectListItem> CourseNamesDropdownList { get; set; }

    public virtual Courseviewmodel Course { get; set; }
}

}

这是我的Courseviewmodel代码

    public class Courseviewmodel
{
    [Key]
    public int CourseId { get; set; }

    public string CourseName { get; set; }

这是我的HoleviewmodelController创建动作

        public ActionResult Create()
    {
        ViewBag.CourseId = new SelectList(db.Courseviewmodels,"CourseId","CourseName");
        return View();
    }

这是我的MVC创建视图

@using (Html.BeginForm()) 

{ @ Html.AntiForgeryToken（）

<div class="form-horizontal">
    <h4>Holeviewmodel</h4>
    <hr />
    @Html.ValidationSummary(true,"",new { @class = "text-danger" })
    <div class="form-group">
        @Html.LabelFor(model => model.HoleNumber,htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.EditorFor(model => model.HoleNumber,new { htmlAttributes = new { @class = "form-control" } })
            @Html.ValidationMessageFor(model => model.HoleNumber,new { @class = "text-danger" })
        </div>
    </div>

    <div class="form-group">
        @Html.LabelFor(model => model.Par,htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.EditorFor(model => model.Par,new { htmlAttributes = new { @class = "form-control" } })
            @Html.ValidationMessageFor(model => model.Par,new { @class = "text-danger" })
        </div>
    </div>

    <div class="form-group">
        @Html.LabelFor(model => model.Length,htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.EditorFor(model => model.Length,new { htmlAttributes = new { @class = "form-control" } })
            @Html.ValidationMessageFor(model => model.Length,new { @class = "text-danger" })
        </div>
    </div>

    <div class="form-group">
        @Html.LabelFor(model => model.strokeIndex,htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.EditorFor(model => model.strokeIndex,new { htmlAttributes = new { @class = "form-control" } })
            @Html.ValidationMessageFor(model => model.strokeIndex,new { @class = "text-danger" })
        </div>
    </div>

    <div class="form-group">
        @Html.LabelFor(model => model.CourseId,htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.DropDownListFor(model => model.Course.CourseId,Model.CourseNamesDropdownList,"Please select from List",new { @class = "form-control" })
            @Html.ValidationMessageFor(model => model.CourseId,new { @class = "text-danger" })
        </div>
    </div>

    <div class="form-group">
        <div class="col-md-offset-2 col-md-10">
            <input type="submit" value="Create" class="btn btn-default" />
        </div>
    </div>
</div>

解决方法

好，所以我通过修改ActionResult创建代码来解决了此问题

        public ActionResult Create()
{
    ViewBag.CourseId = new SelectList(db.CourseViewModels,"CourseId","CourseName");
    return View();
}

收件人

        public ActionResult Create()
    {
        var dbcourse = db.Course.ToList();

        //Make selectlist,which is IEnumerable<SelectListItem>
        var courseNameDropdownList = new SelectList(db.Course.Select(item => new SelectListItem()
        {
            Text = item.CourseName.ToString(),Value = item.CourseId.ToString()
        }).ToList(),"Value","Text");

        // Assign the Selectlist to the View Model   
        var viewCourse = new HoleViewModel()
        {
            Course = dbcourse.FirstOrDefault(),// The Dropdownlist values
            CourseNamesDropdownList = courseNameDropdownList,};

        //ViewBag.CourseId = new SelectList(db.CourseViewModels,"CourseName");
        return View(viewCourse);
    }

这允许填充下拉列表并将其添加到视图中。