I'm wanting to do a simple edit form for our Issue Tracking app. For simplicity, the HttpGet Edit action looks something like this:

    // Issues/Edit/12
    public ActionResult Edit(int id)
    {
        var thisIssue = edmx.Issues.First(i => i.IssueID == id);
        return View(thisIssue);
    }

and then the HttpPost action looks something like this:

    [HttpPost]
    public ActionResult Edit(int id, FormCollection form)
    {
        // this is the dumb part where I grab the object before I update it.
        // concurrency is sidestepped here.
        var thisIssue = edmx.Issues.Single(c => c.IssueID == id);

        TryUpdateModel(thisIssue);
        if (ModelState.IsValid)
        {
            edmx.SaveChanges();

            TempData["message"] = string.Format("Issue #{0} successfully modified.", id);
            return RedirectToAction("Index");
        }

        return View(thisIssue);
    }

Which works wonderfully. However, the concurrency check doesn't work because in the Post, I'm re-retreiving the current entity right before I attempt to update it. However, with EF, I don't know how to use the fanciness of SaveChanges() but attach my thisIssue to the context. I tried to call edmx.Issues.Attach(thisIssue) but I get

The object cannot be attached because it is already in the object context. An object can only be reattached when it is in an unchanged state.

How do I handle concurrency in MVC with EF and/or how do I properly Attach my edited object to the context?

Thanks in advance