ASP.NET MVC Dropdownlist Data Does Not Insert

Question

I have two models and I want to insert a row in the database with a foreign key relationship populated in the DropDownList. The Item model's data insert without problems but ManufacturerID does not get inserted (it inserts null). I could not find why. Update: Uploaded the project to: http://mvcapplication2.codeplex.com/

<div class="editor-label">
   @Html.LabelFor(model => model.ManufacturerID,"Manufacturer")
</div>

<div class="editor-field">
   @Html.DropDownList("ManufacturerID",string.Empty)
   @Html.ValidationMessageFor(model => model.ManufacturerID)
</div>

public class Item
{
   public int ItemID { get; set; }
   public string Serial { get; set; }
   public string ItemName { get; set; }
   public int? ManufacturerID { get; set; }
   public Manufacturer Manufacturer { get; set; }
}

public class Manufacturer
{
   public int ManufacturerID { get; set; }
   public string ManufacturerName { get; set; }
   public List<Item> Items { get; set; }
}

public ActionResult Create()
{
   ViewBag.ManufacturerID = new SelectList(db.Manufacturers, "ManufacturerID", "ManufacturerName");
   return View();
} 

[HttpPost]
public ActionResult Create(Item ıtem)
{
   if (ModelState.IsValid)
   {
      db.Items.Add(ıtem);
      db.SaveChanges();
      return RedirectToAction("Index"); 
   }

   return View(ıtem);
}

is the property value set in your create method during debug? — MUG4N
– MUG4N, Commented Jan 25, 2013 at 20:50
I'm not getting any exceptions. I don't know how to check the property method. It looks like the same like in the MvcMusicStore application; I could not find why it does not insert. The dropdown gets populated with the Manufacturers table. — Bora
– Bora, Commented Jan 25, 2013 at 20:55
Here is the values of the Item in the debug: ItemID=0, ItemName="Item1", Manufacturer=null, ManufacturerID=null, Serial="123" — Bora
– Bora, Commented Jan 25, 2013 at 21:00
@Bora ManufacturerID (according to your example posted above) comes from the Item class and is of type int. Thus it can not be null. Where are you seeing that ManufacturerID is null? In the controller? In the view? In the database only? — jmrnet
– jmrnet, Commented Jan 25, 2013 at 21:07

Shyju · Accepted Answer · 2013-01-25 22:34:59Z

I would prefer to NOT use the domain model in the view. I would create some view models specific to the view. Also, to transfer data from action method (ex : dropdown list), i would use a strongly typed approach, instead of the dynamic viewbag/ viewdata approach.

Create a view model class

public class CreateItemVM
{
  public string SerialNumber { set;get;}
  public int SelectedManufactureID { set;get;}
  public List<SelectListItem> Manufacturers { set;get;}
  public CreateItemVM()
  {
     Manufacturers =new List<SelectListItem>();
  }     
}

Now in your GET action method, create an object of our viewmodel, initialize the relevant values and send to the view.

public ActionResult Create()
{
  var vm=new CreateItemVM();
  vm.Manufacturers=GetManufacturerList();
  return View(vm);
}
private List<SelectListItem> GetManufacturerList()
{
    List<SelectListItem> manuList=new List<SelectListItem>();
    manuList=(from p in  db.Manufacturers
                   select new SelectListItem { 
                                               Value=p.ID.ToString(),
                                               Text=p.Name}
              ).ToList();
    return manuList;
}

Now in our view, which is strongly typed to our Viewmodel,

@model CreateItemVM
@using(Html.Beginform())
{
  @Html.DropDownListfor(x=>x.SelectedManufactureID ,
                                      Model.Manufacturers,"select")
  <input type="submit" />
}

And finally in our POST action method, we will read values from our posted viewmodel and assign it as the property values of our domain object and save it. the selected manufacturers ID value will be in the SelectedManufactureID property of our viewmodel.

[HttpPost]
public ActionResult Create(CreateItemVM model)
{
  if(ModelState.IsValid)
  {
     Item domainObject=new Item();
     domainObject.ManufacturerID =model.SelectedManufactureID ;
     //set other relevant properties also
      db.Items.Add(ıtem);
      db.SaveChanges();
      return RedirectToAction("Index");
  } 
  // reload the dropdown before returning to the view
  model.Manufacturers=GetManufacturerList();
  return View(model);   
}

Thanks for the reply, I know that using a view model is the right way to do this but I'm trying to learn Mvc and could not find where did I do wrong. I'm pretty sure that I'm missing something.

Ricardo Souza · Accepted Answer · 2013-01-25 22:22:34Z

1

Try to make the relationship more explicit, making properties virtual and adding an attribute:

public class Item
{
    ...
    [ForeignKey("Manufacturer")]
    public int? ManufacturerID { get; set; }
    public virtual Manufacturer Manufacturer { get; set; }
}

public class Manufacturer
{
    ...
    public virtual List<Item> Items { get; set; }
}

Edit:

And you can use a more tied way of building the drop down:

@Html.DropDownListfor(x=>x.SelectedManufactureID ,
                                  ViewBag.ManufacturerID as SelectList,"Choose one")

Edit 2:

A better approach is to make a specific model for the view (called ViewModel) to represent data and build the view like @Shyju said.

edited Jan 25, 2013 at 22:22

answered Jan 25, 2013 at 21:15

Ricardo Souza

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1 Comment

Bora Over a year ago

It did not work. Looks like it is a problem with the DropDownList sending the appropriate values. I edited the manufacturerID column via the edit link in the and it updates and shows the manufacturer name. Somehow selecting the manufacturer does not submit the value.

Bora · Accepted Answer · 2013-01-26 23:04:13Z

0

Found the problem. The Viewbag I was sending to the view should be named as ManufacturerID, I was sending Manufacturers and somehow it was not matching although it populated the dropdown.

answered Jan 26, 2013 at 23:04

Bora

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