Chaining multiple classes in a MVC4 view

Question

Let's say I have a model like this (simplified from the original):

public class Location
{
    public int ID { get; set; }
    public string BinNumber { get; set; }
}

public class Item
{
    public int ID { get; set; }
    public string Description { get; set; }
    public virtual Location Bin { get; set; }
}

public class LineOnPickList
{
    public int ID { get; set; }
    public virtual Item Item { get; set; }
}

The usual thing to do here on the LineOfPickList Create view would be to have a dropdownlist that listed all the Item Descriptions and put the selected item in the newly created LineOnPickList record when Create was clicked.

What I need to do however is show a dropdownlist of Location BinNumbers, yet still have the Item associated with that Location in the newly created LineOnPickList record.

How would that be done?

Answer 1

Define a view model for your drop down

public class ItemViewModel
{
    public int ID { get; set; }
    public string BinNumber { get; set; }
}

Then build the drop down list data in your controller action as follows

public class CreateLineOnPickListViewModel
{
    public int ItemId { get; set; }
    public IEnumerable<ItemViewModel> Items { get; set; }
}

public ActionResult Create()
{
    var model = new CreateLineOnPickListViewModel();
    model.Items = db.Items
          .Select(i => new ItemViewModel { ID = i.ID, BinNumber = i.Bin.BinNumber });

    return View(model);
}

Then in your view

@model CreateLineOnPickListViewModel

@Html.DropDownListFor(m => m.ItemId, new SelectList(Model.Items, "ID", "BinNumber"), "-")

Then your post action method in your controller would look like this

public ActionResult Create(CreateLineOnPickListViewModel model)
{
    var item = new Item { ID = model.ItemID };
    db.Items.Attach(item);

    var lineOnPickList = new LineOnPickList { Item = item };

    db.SaveChanges();

    return View(model);
}