public ActionResult Edit(Presentation presentation)
 {
     if (ModelState.IsValid)
     {
         db.Entry(presentation).State = EntityState.Modified;
         db.SaveChanges();
         return RedirectToAction("Index");
     }
     return View(presentation);
 }
        public ActionResult Create(Presentation presentation)
        {
            if (ModelState.IsValid)
            {
                db.Presentations.Add(presentation);
                db.SaveChanges();
                return RedirectToAction("Index");
            }

            return View(presentation);
        }