如何从一个表中获取 Id 并将其保存到 ASP.NET Core 中的另一个表，存储库模式

Question

这是预约考试服务：

public int AddSchedule(ScheduleExamViewModel schedule)
{
        var newSchedule = new ScheduleExam()
        {
            ExamDate = schedule.ExamDate,
            SubjectId = schedule.SubjectId,
            StudentId = schedule.StudentId,
            Status = schedule.Status
        };

        _context.ScheduleExams.Add(newSchedule);
        _context.SaveChanges();

        return newSchedule.Id;
}

这是安排考试控制器：

// GET: ScheduleExamController/Create
public IActionResult Create()
{
    var model = new ScheduleExamViewModel();

    ViewBag.Subject = new SelectList(_isubject.GetSubject(), "Id", "Name");
    ViewBag.Student = new SelectList(_istudent.GetStudent(), "Id", "Name");

    return View(model);
}

// POST: ScheduleExamController/Create
[HttpPost]
[ValidateAntiForgeryToken]
public IActionResult Create(ScheduleExamViewModel schedule)
{
    if (ModelState.IsValid)
    {
        int id = _ischeduleExam.AddSchedule(schedule);

        if (id > 0)
        {
            return RedirectToAction(nameof(Create));
        }
    }

    ViewBag.Subject = new SelectList(_isubject.GetSubject(), "Id", "Name");
    ViewBag.Student = new SelectList(_istudent.GetStudent(), "Id", "Name");

    return View(schedule);
}

我想通过点击“安排新考试”获取学生 ID 并将其保存到安排考试表中

这是学生表的index.cshtml：

<table class="table table-hover table-bordered table-condensed">
            <thead class="table-color text-white">
                <tr>
                    <th>
                        @Html.DisplayNameFor(model => model.Id)
                    </th>
                    <th>
                        @Html.DisplayNameFor(model => model.Name)
                    </th>
                    <th>
                        @Html.DisplayNameFor(model => model.LastName)
                    </th>
                    <th>
                        @Html.DisplayNameFor(model => model.Email)
                    </th>
                    <th>Schedule New Exam</th>
                    <th>Properties</th>

                </tr>
            </thead>
            <tbody>
                @foreach (var item in Model)
                {
                <tr>
                    <td>
                        @Html.DisplayFor(modelItem => item.Id)
                    </td>
                    <td>
                        @Html.DisplayFor(modelItem => item.Name)
                    </td>
                    <td>
                        @Html.DisplayFor(modelItem => item.LastName)
                    </td>
                    <td>
                        @Html.DisplayFor(modelItem => item.Email)
                    </td>
                    <td>
                        <a asp-action="Create" asp-controller="ScheduleExam", asp-route-id="@item.Id">Schedule New Exam</a>
                    </td>
                    <td>
                        @Html.ActionLink(" ", "Edit", new { id = item.Id }, new { @class = "fa fa-edit", title = "Edit" }) &nbsp;|&nbsp;
                        @Html.ActionLink(" ", "Details", new { id = item.Id }, new { @class = "fa fa-info-circle", title = "More details" }) &nbsp;|&nbsp;
                        @Html.ActionLink(" ", "Delete", new { id = item.Id }, new { @class = "fa fa-trash", title = "Delete" })
                    </td>
                </tr>
                }
            </tbody>
        </table>

这是安排考试的create.csthml页面：

 <form asp-action="Create">
        <div asp-validation-summary="ModelOnly" class="text-danger"></div>

        <div class="form-group">
            <label asp-for="ExamDate" class="control-label"></label>
            <input asp-for="ExamDate" class="form-control" />
            <span asp-validation-for="ExamDate" class="text-danger"></span>
        </div>
        <div class="form-group">
        <label asp-for="StudentId" class="control-label"></label>
        <input asp-for="StudentId" class="form-control" value="@ViewBag.model.Id" />
        <span asp-validation-for="StudentId" class="text-danger"></span>
    </div>
        <div class="input-group">
            <div class="input-group-prepend">
                <span class="input-group-text"><strong>Subject:</strong></span>
            </div><br />
            <select asp-for="SubjectId" class="form-control input-hover" asp-items="ViewBag.Subject">
                <option value="">Please choose a subject...</option>
            </select>
            <span asp-validation-for="SubjectId " class="text-danger"></span>
        </div><br />
        <div class="form-group">
            <input type="submit" value="Create" class="btn btn-primary" />
        </div>
    </form>

但是当我点击 Student 表的 index.cshtml 中的 Schedule New Exam 时，我得到了这个错误：

RuntimeBinderException：无法对空引用执行运行时绑定 CallSite.Target(闭包, CallSite, 对象)

CallSite.Target（闭包，CallSite，对象） System.Dynamic.UpdateDelegates.UpdateAndExecute1(CallSite 站点, T0 arg0)
Create.cshtml 中的 AspNetCore.Views_ScheduleExam_Create.b__22_0() +

<input asp-for="StudentId" class="form-control" value="@ViewBag.model.Id" />

请详细解决，我正在使用 ASP.NET Core 3.1 MVC，使用存储库模式。

谢谢

Answer 1

首先，您应该在 Create-Action 中获得一个 Id 并为学生设置：

public IActionResult Create(int Id)
{
    var model = new ScheduleExamViewModel();
    
    ViewBag.Subject = new SelectList(_isubject.GetSubject(), "Id", "Name");
    ViewBag.Student = new SelectList(_istudent.GetStudent(), "Id", "Name" , Id);

    return View(model);
}

其次，我在您的视图中找不到学生的下拉列表。我认为您应该在 ViewModel 的控制器中设置 Id。

var model = new ScheduleExamViewModel();
mode.Id = Id;

第三，您将模型传递给视图，您可以从模型中获取信息。

@model ScheduleExamViewModel
<input asp-for="StudentId" class="form-control" value="@Model.Id" />