Question

I am trying to create an Item that has an ItemType coming from another table. I am unable to get back the actual Type object from the Create page. This is the code I have tried:

Models:

public class ItemType {
    public int Id { get; set; }
    [Required]
    public string Name { get; set; }
    public virtual ICollection<Item> Item{ get; set; }
}

public class Item {
    public int Id { get; set; }
    [Required]
    public string Name { get; set; }       
    public virtual ItemType ItemType { get; set; }
}

In the ItemController, this is my create code:

    public ActionResult Create() {
        var itemTypeRepo = new ItemTypeRepository(context);
        ViewBag.ItemTypes = new SelectList(itemTypeRepo.GetAll(), "ID", "Name");
        return View();
    }

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

In my Create.cshtml view I have tried:

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

This returns no value at all and throws an error “The value ‘X’ is invalid.” Where X is the ID of the ItemType I selected.
And

<div class="editor-field">
    @Html.DropDownListFor(x => x.ItemType.Id, (SelectList)ViewBag.ItemType)
    @Html.ValidationMessageFor(model => model.ItemType) 
</div>

This creates a stub ItemType object with the correct ID but does not insert it into the database since the object is not fully loaded. If I look at ModelState object, I find that there is an error that the Name field is missing from ItemType object.

I also attempted to solve the problem using the second .cshtml code and adding this code:

public ActionResult Create(Item item) { 
    item.ItemType = context.ItemTypes.Find(item.ItemType.Id);
    if (ModelState.IsValid)

This does not change the value of ModelState.IsValid from false even through it should.

What do I need to do to get this to work?

Answer 1

You should add a property ItemTypeId to your Item entity so that it acts as a foreign key.

public class Item
{
    public int Id { get; set; }
    [Required]
    public string Name { get; set; }
    public int ItemTypeId { get; set; }

    [ForeignKey("ItemTypeId")]
    public virtual ItemType ItemType { get; set; }
}

You can then use that property for the dropdownlist:

<div class="editor-field">
    @Html.DropDownListFor(x => x.ItemTypeId, (SelectList)ViewBag.ItemType)
    @Html.ValidationMessageFor(model => model.ItemType) 
</div>