public ActionResult Create(Achievement achievement)
        {
            if (ModelState.IsValid)
            {
                if (string.IsNullOrEmpty(achievement.ImageUrl))
                {
                    achievement.ImageUrl = DefaultImgUrl;
                }
                db.Achievements.Add(achievement);
                db.SaveChanges();
                return RedirectToAction("Index");
            }

            return View(achievement);
        }
 public ActionResult Edit(Achievement achievement)
 {
     if (ModelState.IsValid)
     {
         db.Achievements.Update(achievement);
         db.SaveChanges();
         return RedirectToAction("Index");
     }
     return View(achievement);
 }