public ActionResult List(string prefix)
        {
            //var model = _db.Where(c => prefix == null || c.FirstName.ToLower().StartsWith(prefix.ToLower())).ToList();
            var contacts = _db.Where(c => prefix == null || c.FirstName.ToLower().StartsWith(prefix.ToLower())).ToList();
            var letters = _db.Select(c=> c.FirstName.Substring(0, 1).ToUpper()).Distinct().OrderBy(letter => letter).ToList();
            var model = new ContactViewModel
            {
                SelectedLetters = letters,
                Contacts = contacts
            };

            return View(model);
        }
        public ActionResult List(string prefix)
        {
            var _db = new ContactBUS().GetContacts();
            var contacts = _db.Where(c => prefix == null || c.FirstName.ToLower().StartsWith(prefix.ToLower())).ToList();
            var letters = _db.Select(c => c.FirstName.Substring(0, 1).ToUpper()).Distinct().OrderBy(letter => letter).ToList();
            var model = new ContactViewModel
            {
                SelectedLetters = letters,
                Contacts = contacts,
                SelectedLetter = prefix != null ? prefix.ToUpper() : String.Empty
            };
            
            //var model = new List<Contact>();
            //foreach(var contact in _db)
            //    if(prefix == null || contact.FirstName.ToLower().StartsWith(prefix.ToLower()))
            //        model.Add(contact);

            return View(model);
        }
        public ActionResult List(int id, string prefix)
        {
            //if (prefix == null)
            //{
            //    prefix = 'A'.ToString();
            //}
            var _db = new ContactBUS().GetContacts();
            var contacts = _db.Where(c => prefix == null || c.FirstName.ToLower().StartsWith(prefix.ToLower())).ToList();
            
            var letters = _db.Select(c => c.FirstName.Substring(0, 1).ToUpper()).Distinct().OrderBy(letter => letter).ToList();

            var model = new ContactViewModel
            {
                Contacts = contacts,
                SelectedLetters = letters,
                SelectedLetter = prefix != null ? prefix.ToUpper() : String.Empty,
                lastId = id
            };
            return View(model);
        }