public async Task<ActionResult> Create(Book c)
 {
     if(ModelState.IsValid)
     {
         await db.Books.InsertOneAsync(c);
         return RedirectToAction("index");
     }
     return View(c);
 }
        public async Task<ActionResult> Edit(Book c)
        {
            if(ModelState.IsValid)
            {
                await db.Books.ReplaceOneAsync(new BsonDocument("_id", new ObjectId(c.Id)), c);
                return RedirectToAction("Index");

            }
            return View(c);
        }