没有具有'Userlist‘键的'IEnumerable<SelectListItem>’类型的IEnumerable<SelectListItem>项

Question

我的用户模型

    [Key]
    public int UserId { get; set; }
    [Required]
    [DisplayName("First Name")]
    public string FirstName { get; set; }
    [Required]
    [DisplayName("Last Name")]
    public string LastName { get; set; }

    public virtual List<DptCRP> DptCRPs { get; set; }

我的病人模型

        [Key]
        [Required]
        [DisplayName("Registration No")]
        public string PatientRegNo { get; set; }
        [Required]
        [DisplayName("Patient Name")]
        public string PatientName { get; set; }
        [Required]
        [DisplayName("Father Name")]
        public string FatherName { get; set; }
        public string ReferDpt { get; set; }

        public virtual List<DptCRP> DptCRPs { get; set; }

My DptCRP模型(在此模型中使用UserId nad PatientRegNo作为外键)

    [Key]
    public int CRPId { get; set; }

    [DisplayName("Provisional Diagnosis")]
    public string ProvisionalDiagnosis { get; set; }
    [DisplayName("Progress Report")]
    public string ProgressReport { get; set; }

    [Required]
    public int UserId { get; set; }
    public virtual User User { get; set; }

    [Required]
    public string PatientRegNo { get; set; }
    public virtual Patient Patient { get; set; }

我的部门财务主任

[HttpGet]
    public ActionResult AddDptCRP()
    {
        var user = (from p in userdb.Users
                    where p.UserType == "doctor"
                    select p.UserId).ToList();
        ViewBag.Userlist = new SelectList(user, "UserId");
        var patient = (from p in patientdb.Patients
                    where p.ReferDpt == "dptcrp"
                    select p.PatientRegNo).ToList();
        ViewBag.Patientlist = new SelectList(patient, "PatientRegNo");
        return View();
    }

    [HttpPost]
    public ActionResult AddDptCRP(DptCRP dptcrp)
    {
        try
        {
            if (ModelState.IsValid)
            {
                dptdb.DptCRPs.Add(dptcrp);
                dptdb.SaveChanges();
                return RedirectToAction("ListDptCRP");
            }
            var user = (from p in userdb.Users
                        where p.UserType == "doctor"
                        select p.UserId).ToList();
            ViewBag.Userlist = new SelectList(user, "UserId");
            var patient = (from p in patientdb.Patients
                           where p.ReferDpt == "dptcrp"
                           select p.PatientRegNo).ToList();
            ViewBag.Patientlist = new SelectList(patient, "PatientRegNo");
            return View(dptcrp);
        }
        catch 
        {
            return View();
        }
    }

当我试图在我的DptCRP中添加数据时，它会显示错误

没有具有'Userlist‘键的'IEnumerable’类型的IEnumerable项

我的AddDptCRP视图看起来就像

@model FinalYear.Models.DptCRP
 @using (Html.BeginForm()) 
    {
    @Html.AntiForgeryToken()
    <div class="form-horizontal">
        <h4>DptCRP</h4>
        <hr />
        @Html.ValidationSummary(true, "", new { @class = "text-danger" })
        <div class="form-group">
            @Html.LabelFor(model => model.ProvisionalDiagnosis, htmlAttributes: new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.EditorFor(model => model.ProvisionalDiagnosis, new { htmlAttributes = new { @class = "form-control" } })
                @Html.ValidationMessageFor(model => model.ProvisionalDiagnosis, "", new { @class = "text-danger" })
            </div>
        </div>
    <div class="form-group">
            @Html.LabelFor(model => model.ProgressReport, htmlAttributes: new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.EditorFor(model => model.ProgressReport, new { htmlAttributes = new { @class = "form-control" } })
                @Html.ValidationMessageFor(model => model.ProgressReport, "", new { @class = "text-danger" })

        </div>
    </div>

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

    <div class="form-group">
        @Html.LabelFor(model => model.PatientRegNo, "PatientRegNo", htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.DropDownList("Patientlist", null, htmlAttributes: new { @class = "form-control" })
            @Html.ValidationMessageFor(model => model.PatientRegNo, "", 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>
}

Answer 1

下面的查询返回int的列表。

var user = (from p in userdb.Users
            where p.UserType == "doctor"
            select p.UserId).ToList();

问题从您使用的构造函数开始。

ViewBag.Userlist = new SelectList(user, "UserId");

这个构造函数

使用列表的指定项和选定的值初始化类的新实例。

与其使用此构造函数，不如使用以下构造函数：

ViewBag.Userlist = new SelectList(user, "UserId", "UserId");

哪一个

使用列表的指定项、数据值字段和数据文本字段来初始化类的新实例。

在您的示例中，数据值字段和数据文本字段将是相同的。

有关SelectList的这些构造函数和其他构造函数的更多信息，请查看这里。

在视图中，您必须进行另一项更改。

这

 @Html.DropDownList("Userlist", null, htmlAttributes: new { @class = "form-control"})

应该写成这样：

 @Html.DropDownList("Userlist", ViewBag.Customerlist as IEnumerable<SelectListItem>,htmlAttributes: new { @class = "form-control"})

这里使用的构造函数如下：

public static MvcHtmlString DropDownList(
    this HtmlHelper htmlHelper,
    string name,
    IEnumerable<SelectListItem> selectList,
    IDictionary<string, object> htmlAttributes
)

因此，如果将null作为第二个参数传递，则没有任何选择列表。有关此html助手的更多信息，请查看这里。最后但并非最不重要的是，请注意as操作符的使用。我们使用它是因为我们必须将我们的对象转换成某种类型的IEnumerable<SelectListItem>，以便将它作为参数传递给我们的html助手。ViewData是ViewDataDictionary类型，它是一个IDictionary<string, object>。这就是为什么你必须转换你的ViewBag.Userlist。