C#

Edit View
/////////////////////////////////////////////////////////////////

<tr>
  <td>@Html.LabelFor(model=>model.Category.ID, "Category")</td>                
  <td>
      @Html.DropDownListFor(model => model.ProductCategories, 
      ViewBag.categoryList as IEnumerable<SelectListItem>,
      (string)ViewBag.ProductCategoryName)
  </td> 
</tr>

/////////////////////////////////////////////////////////////////

Edit Method in EditController

       [HttpPost]
        public ActionResult Edit(ProductViewModel pvm)
        {
            ProductServiceClient psc = new ProductServiceClient();
            psc.EditProduct(pvm.Product);
            return RedirectToAction("Index");
        }

public class ProductViewModel
{
    public Product Product
    { get;set;}

    public Category Category
    {get;set;}

    public ProductCategory ProductCategory
    {get;set;}

    private IEnumerable<SelectListItem> productCategories;

    public IEnumerable<SelectListItem> ProductCategories
    {
        get
        {
            return productCategories ?? new List<SelectListItem>();
        }
        set
        {
            productCategories = value;
        }
    }
}

public class Product
{
    [Display(Name = "ID")]
    public int ID { get; set; }

    [Display(Name = "Name")]
    public string Name { get; set; }

    [Display(Name = "Price")]
    public decimal Price { get; set; }

    [Display(Name = "CategoryID")]
    public int CategoryID { get; set; }
}

public class Category
{
    [Display(Name = "ID")]
    public int ID { get; set; }

    [Display(Name = "Name")]
    public string Name { get; set; }
}

public void MyMethod(string id)
{
 List<Product> _products = new List<Product>();
 List<Category> _categories = new List<Category>();

_products = psc.FindAllProducts();//Returns a list of Products
_categories = psc.FindAllCategories();//Returns a list of Categories

var _productCategories =
     from c in _categories
     join p in _products
     on c.ID equals p.CategoryID
     select new {
       p.ID, p.Name, p.Price,
       p.Quantity, p.CategoryID,
       _categoryID = c.ID,
      _categoryName = c.Name
    };

var selectedCat = _productCategories
    .Where
    (x => x._categoryID.ToString() == id)
    .SingleOrDefault()._categoryName;
}

public class Person : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;
    private void NotifyPropertyChanged([CallerMemberName]string propertyName = null)
    {
        // Is it really needed, to make a copy?  *1) 
        var handler = PropertyChanged;
        if (handler != null)
        {
            handler(this, new PropertyChangedEventArgs(propertyName));
        }
    }
    // ....
}