LINQ to SQL - Save an entity without creating a new DataContext?

Question

I get this error

Cannot add an entity with a key that is already in use

when I try to save an Item

[AcceptVerbs(HttpVerbs.Post)]
public ActionResult Edit(Item item)
{
  Global.DataContext.Items.Attach(item);
  Global.DataContext.SubmitChanges();

  return View(item);
}

That's because I cannot attach the item to the global DataContext.

Is it possible to save an item without creating a new DataContext, and without having to assign each field of the item manually?

(I am very new to LINQ)

EDIT: I realised static DataContext would cause problems thanks to the comments below, it is now like this

public static AbcDataContext DataContext
{
  get
  {
    if (!HttpContext.Current.Items.Contains("DataContext"))
      HttpContext.Current.Items["DataContext"] = new AbcDataContext(ConnectionString);
    return (AbcDataContext)HttpContext.Current.Items["DataContext"];
  }
}

(Rex might not agree to that, but I can't be bothered changing the whole code at the moment - may be later)

Answer 1

Don't have a global/static DataContext, that is setting yourself up for pain. A DataContext should represent a single logical transaction ("get in, do x/y/z and get out"). They are cheap to create and easy to dispose; there is absolutely no reason to try to minimize them, much less keep a global/static one.