public void InsertOrUpdate(Document document)
 {
     if (document.Id == default(int)) {
         // New entity
         context.Documents.Add(document);
     } else {
         // Existing entity
         context.Entry(document).State = EntityState.Modified;
     }
 }
 public ActionResult Create(Document document)
 {
     if (ModelState.IsValid) {
         documentRepository.InsertOrUpdate(document);
         documentRepository.Save();
         return RedirectToAction("Index");
     } else {
         ViewBag.PossibleGroups = groupRepository.All;
         return View();
     }
 }