c# - 为访问所选下拉列表 Id asp.net mvc 的列表中的每条记录保存一个项目

Question

我有一张包含 Instructors、Events 和一个名为 InstructorEvents 的表，用于保存可能要参加事件的讲师。

我生成了一个 View ，其中列出了讲师和每个讲师旁边的下拉列表以选择是、否或可能参加该事件。

这是它的 Controller :

public ViewResult PreRegister(int eventId)
    {
        //Find Event
        var selectedEvent = db.Events.FirstOrDefault(t => t.EventId == eventId);
        //Instructors List        
        IEnumerable<Instructor> currentInstructors;
        //Generate a list of the current Instructors
        using (ApplicationDbContext context = new ApplicationDbContext())
        {
            currentInstructors = context.Instructors
                .Where(s => s.Left < DateTime.Now)
                .OrderBy(s => s.LastName)
                .ToList();
        }
        EventPreRegisterViewModel viewModel = new EventPreRegisterViewModel
        {
            EventId = selectedEvent.EventId,
            EventName = selectedEvent.Name,
                      InstructorRegisterListViewModels =
                            currentInstructors.Select(
                                x => new InstructorRegisterListViewModel { InstructorId = x.InstructorId, Name = x.FirstName + " " + x.LastName, Attendances = db.Attendances.Where(t => t.Dormant == false && t.AttendanceId == 1 || t.AttendanceId == 2 || t.AttendanceId == 3).ToList() }).ToArray()
        };
        return View(viewModel);
    }

风景

@model YFA.ViewModels.EventPreRegisterViewModel

@{
ViewBag.Title = "Pre Register for Event";
}

<h2>Pre Register for @Html.DisplayFor(model => model.EventName)</h2> 
@using (Html.BeginForm())
{
@Html.AntiForgeryToken()

<div class="form-horizontal">
    <hr />
    @Html.ValidationSummary(true, "", new { @class = "text-danger" })

    @Html.HiddenFor(model => model.EventId)
    <h3>Instructors</h3>
    <div class="col-md-offset-1">
        @for (int i = 0; i < Model.InstructorRegisterListViewModels.Count();  i++)
        {
            <div class="form-group">
                <div class="row">
                    @Html.HiddenFor(x => Model.InstructorRegisterListViewModels[i].InstructorId)
                    <div class="col-md-2">
                        @Html.LabelFor(x =>  Model.InstructorRegisterListViewModels[i].Name, Model.InstructorRegisterListViewModels[i].Name)
                    </div>
                    <div class="col-md-2">
                        @Html.DropDownListFor(model => model.InstructorRegisterListViewModels[i].AttendanceId, new SelectList(Model.InstructorRegisterListViewModels[i].Attendances, "AttendanceId", "AttendanceName", 0), "Please Select", new { @class = "form-control" })
                    </div>
                </div>
            </div>
        }
    </div>

    <div class="form-group">
        <div class="col-md-offset-1 col-md-10">
            <input type="submit" value="Save" class="btn btn-default" />
        </div>
    </div>
</div>
}
<div>
@Html.ActionLink("Back to Event List", "Index")
</div> 

这是我对 post 方法的尝试，该方法为每个讲师在 InstructorEvent 表中添加一条记录，但目前我已经手动写入 AttendanceId，而不是从下拉列表中引用选定的 Id。

    [HttpPost]
    [ValidateAntiForgeryToken]
    public ActionResult PreRegister(EventPreRegisterViewModel viewModel)
    {
            // Get list of instructors 
            IEnumerable<int> instructorIds = viewModel.InstructorRegisterListViewModels.Select(x => x.InstructorId);
            // Find the event
            Event eventSel = db.Events.Find(viewModel.EventId);
            // Copy instructors in the event
            IEnumerable<InstructorEvent> instructorEvents = eventSel.InstructorEvents.ToList();
            // Remove previous instructors
            foreach (InstructorEvent previousInstructor in instructorEvents)
            {
                db.InstructorEvents.Remove(previousInstructor);
            }
            // Add new club interests
            foreach (int InstructorId in instructorIds)
            {
                Instructor instructor = db.Instructors.Find(InstructorId);
 //THIS IS THE SECTION I'M STRUGGLING WITH
                var newInstructorEvent = new InstructorEvent { EventId = eventSel.EventId, InstructorId = instructor.InstructorId, AttendanceId = 1};

                db.InstructorEvents.Add(newInstructorEvent);
            }
            // Save new club interests           
            db.SaveChanges(); 
        return RedirectToAction("Index");
    }

Answer 1

为什么不只是循环遍历 View 模型？

[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult PreRegister(EventPreRegisterViewModel viewModel)
{
    // Find the event
    var eventSel = db.Events.Find(viewModel.EventId);
    // Remove previous instructors
    foreach (var previousInstructor in eventSel.InstructorEvents)
    {
        db.InstructorEvents.Remove(previousInstructor);
    }
    foreach (var model in viewModel.InstructorRegisterListViewModels)
    {
        var newInstructorEvent = new InstructorEvent { EventId = eventSel.EventId, InstructorId = model.InstructorId, AttendanceId = model.AttenanceId };
        db.InstructorEvents.Add(newInstructorEvent);
    }
    // Save new club interests           
    db.SaveChanges();
    return RedirectToAction("Index");
}