c# - 无法将对象添加到 context.DbSet。保存更改不起作用

Question

我在 Controller 中有这个 GET 方法:

public ActionResult Reserve(int id)
{
    ViewBag.staffID = new SelectList(context.Staffs, "staffID", "fName");
    ViewBag.roomID = id;
    return View();
}

对应 View :

@model _00002165.Models.Reservation

@{
    ViewBag.Title = "Reserve";
}

<h2>Reserve</h2>
 @using (Html.BeginForm()) {
    @Html.ValidationSummary(true)


    <div class="editor-label">
        <label>Room Number</label>
    </div>
    <div class="editor-field">
        <input type="text" value="@ViewBag.roomID" readonly name="roomID"/>
    </div>

    <div class="editor-label">
        @Html.LabelFor(model => model.fromDate)
    </div>
    <div class="editor-field">
        @Html.TextBoxFor(model => model.fromDate)
        @Html.ValidationMessageFor(model => model.fromDate)
    </div>
    <div class="editor-label">
        @Html.LabelFor(model => model.toDate)
    </div>
    <div class="editor-field">
        @Html.TextBoxFor(model => model.toDate)
        @Html.ValidationMessageFor(model => model.toDate)
    </div>

    <div class="editor-label">
        <label>Staff:</label>
    </div>
    <div class="editor-field">
        @Html.DropDownList("staffID", "Select Staff")
        @Html.ValidationMessageFor(model => model.staffID)
    </div>

   <button type="submit">Reserve</button>
}

我想使用这些 POST 方法保存来自这些输入的数据:

[HttpPost]
public ActionResult Reserve(Reservation res)
{
    if (ModelState.IsValid)
    {
        var customer = context.Customers.First(x => x.username == User.Identity.Name);
        res.customerID = customer.customerID;
        context.Reservation.Add(res);
        context.Entry(res).State = EntityState.Modified;
        context.SaveChanges();
        return RedirectToAction("Index");
    }
}

这给我以下错误:

Store update, insert, or delete statement affected an unexpected number of rows (0).

人们建议我将 @Html.HiddenFor(model => model.reservationID) 添加到我的 View 中。

但是 model.reservationID 是空的。

我该如何解决这个问题？ 请帮忙

Answer 1

您不应该将数据传输对象传递到您的 View 或从您的 View 传出。使用将返回所需 DTO 的 ToModel 方法创建 View 模型。添加到上下文中，您不需要更改状态。

使用这个

context.Reservation.Add(res);
context.SaveChanges();

删除

context.Entry(res).State = EntityState.Modified;

如果您正在尝试更新，请从数据库中提取记录，进行更改并调用 SaveChanges