Asp.net mvc ASP.NET MVC 5与DropDownList的一对多关系

我试图实现一个下拉列表，通过一对多关系选择项目

当表单发回控制器时，

package.Platform

对象为空，所以我不知怎么搞砸了映射

/Models/Package.cs

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

    ...

    public Platform Platform {get; set;}
}

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

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

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

[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);
}

/Models/Platform.cs

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

    ...

    public Platform Platform {get; set;}
}

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

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

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

[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);
}

/Controllers/PackagesController.cs

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

    ...

    public Platform Platform {get; set;}
}

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

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

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

[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);
}

（为了简洁起见，省略了FKs）

---

因此，我需要获取

package.Platform

值以正确发布，在

PackagesController

的

Edit（）

方法中获取它，并将其保存

您试图将下拉列表绑定到复杂属性。只能绑定到值类型。它需要是

@Html.DropDownListFor（m=>model.Platform.ID，

，当前当您发回时，

DefaultModelBinder

将尝试设置

package.Platform=“1”

（或“2”）这将失败，因此

平台

的值为

空

注意

模型状态

将始终无效，因为您在

平台.Name

属性上有

[必需的]

属性（您没有绑定到

名称

属性，因此它将始终为

空

，因此无效）@StephenMuecke太好了！我现在在我的POST操作中获得Package.Platform对象。但是，它没有在SaveChanges（）上保存到数据库。下面是生成的SQL:UPDATE[dbo].[Packages]SET[Name]=@0、[Description]=@1、[Version]=@2、[Filename]=@3、[IsPublished]=@4、[ReleaseNotesURL]=@5其中（[ID]=@6）--注意平台ID丢失。我不使用EF，因此无法确定，但我怀疑

包

需要包含外键/导航属性-

public int Platform_ID{get；set；}public virtual Platform{get；set；}

-您将下拉列表绑定到

平台ID

我认为导航属性应该是隐式的，但我会尝试一下。