@ Html.DropDownList仅返回1个值

Question

I am trying to learn MVC ASP.Net, a step in the tutorial advises writing the following code to return all items in the specified list to a dropdown allowing the user to select the required item.

Basic Explanation Drop down list only shows the current item returned eg if the URL is details/2 only 'Pizza' is returned in the list rather than all items in the 'MenuGroups' list. Basic Explanation

Although the code below does work to an extent it does not work the way I am shown in the video, I have even gone as far as going to the website and copying his exact code but I still receive different results and I cannot work out why.

http://cop4834.pbworks.com/w/page/106053825/Menu%20Case%20Study%20Part%204%20-%20Generating%20a%20Javascript%20call%20from%20a%20Razor%20Object

As you can see (If you have time to watch the video the demonstration is at 3:49) all menu groups are returned, my code displays only whatever is passed in via the URL?

    <dt>
     Select a Menu Group
    </dt>

    <dd>
       @Html.DropDownList("MenuGroup", new SelectList(Model.MenuGroups,
          "MenuGroupId", "MenuGroupTitle"),
          new { onchange = "selectMenuGroup()" })
    </dd>

'MenuGroups' is a virtual list created from the Model 'Menu'

    public virtual List<MenuGroup> MenuGroups { get; set; }

The controller is as below:

    public ActionResult FullDetails(int? id)
    {
        if (id == null)
        {
            return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
        }
        Menu menu = db.Menus.Find(id);
        if (menu == null)
        {
            return HttpNotFound();
        }
        return View(menu);
    }

Apologies if this is too long or missed any information, I have looked in to this for many hours before posting but I can only find people saying to use @Html.DropDownListFor instead but I already have a list and so would like to use the above method (and also find out my mistake).

Thanks in advance for any advice.

Answer 1

First make sure that MenuGroups contains multiple items for your selected record.

Then what you can do is replace

public ActionResult FullDetails(int? id)
{
    if (id == null)
    {
        return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
    }
    Menu menu = db.Menus.Find(id);
    if (menu == null)
    {
        return HttpNotFound();
    }
    return View(menu);
}

with

public ActionResult FullDetails(int? id)
{
    if (id == null)
    {
        return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
    }
    Menu menu = db.Menus.Include(r => r.MenuGroups).FirstOrDefault(r => r.Id == id);
    if (menu == null)
    {
        return HttpNotFound();
    }
    return View(menu);
}

Since MenuGroups is a navigation property, you can eager load it by specifying Include(r => r.MenuGroups) . AFAIK Find only returns the entity not including the navigation properties and it is not usable together with Include . The reason why EF uses the virtual keyword is to allow lazy loading on the property. See Lazy Loading vs Eager Loading for more info.