DbUpdateConcurrencyException will not be raised for entity framewrok

public ActionResult Edit(int id, FormCollection collection)
{
    Class c = repository.GetClass(id);
    try
    {
        if (TryUpdateModel(c))
        {
            epository.Save();
            return RedirectToAction("Details", new { id = c.ClassID });
        }
    }

    catch (DbUpdateConcurrencyException ex)
    {
        var entry = ex.Entries.Single();
        var databaseValues = (Class)entry.GetDatabaseValues().ToObject();
        var clientValues = (Class)entry.Entity;
        if (databaseValues.ClassName != clientValues.ClassName)
            ModelState.AddModelError("Name", "Current value: "
            + databaseValues.ClassName);

        ModelState.AddModelError(string.Empty, "The record you attempted to edit "
        + "was modified by another user after you got the original value. The "
        + "edit operation was canceled and the current values in the database "
        + "have been displayed. If you still want to edit this record, click "
        + "the Save button again. Otherwise click the Back to List hyperlink.");
        c.Timestamp = databaseValues.Timestamp;
    }
    catch (DataException)
    {
        //Log the error (add a variable name after Exception)
        ModelState.AddModelError(string.Empty, "Unable to save changes. Try again, and if the problem persists contact your system administrator.");
    }

    return View(c);
}