Question

我正在尝试实施下拉列表，通过一对多关系选择项目。

当表单被POST回控制器时，package.Platform对象为空，所以我以某种方式搞砸了映射。

/Models/Package.cs

public class Package 
{
    public int ID {get; set;}

    ...

    public Platform Platform {get; set;}
}

/Models/Platform.cs

public class Platform
{
    public int ID { get; set; }

    [Required]
    public string Name { get; set; }

    public override string ToString()
    {
        return Name;
    }
}

/Controllers/PackagesController.cs

[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Edit(
    [Bind(Include = "ID,Name,Description,Version,Filename,Platform,IsPublished,ReleaseNotesURL")] Package package)
{
    if (ModelState.IsValid)
    {
        package.Version = VersionParser.ParseVersion(package.Filename).ToString();
        db.Entry(package).State = EntityState.Modified;
        db.SaveChanges();
        return RedirectToAction("Index");
    }

    PopulatePlatformsDropDownList(package.Platform.ID); //<<-- package.Platform is null

    return View(package);
}

...

private void PopulatePlatformsDropDownList(int? selectedPlatform)
{
    var platforms = from d in db.Platforms
                    orderby d.Name
                    select d;
    ViewBag.Platforms = new SelectList(platforms, "ID", "Name", selectedPlatform);
}

/Views/Packages/Edit.cshtml

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

哪个发出此HTML：

<select id="Platform" name="Platform" class="valid">
    <option value="1">Option One</option>
    <option value="2">Option Two</option>
</select>

该关系在SQL中保持如下：

CREATE TABLE [dbo].[Packages](
    [ID] [int] IDENTITY(1,1) NOT NULL,
    [Name] [nvarchar](100) NOT NULL,
    ...
    [Customer_ID] [int] NULL,
    [Platform_ID] [int] NULL
...

CREATE TABLE [dbo].[Platforms](
    [ID] [int] IDENTITY(1,1) NOT NULL,
    [Name] [nvarchar](max) NOT NULL

（为简洁省略了FK）

因此，我需要正确地获取package.Platform值，使用Edit() PackagesController方法获取它，并将其保存。

ASP.NET MVC 5与DropDownList的一对多关系

0 个答案: