public async Task <IActionResult> OnGetAsync(int?id)
        {
            if (id == null)
            {
                return(NotFound());
            }

            KassaBon = await _context.KassaBonnen
                       .Include(k => k.Winkel).SingleOrDefaultAsync(m => m.Id == id);

            KassaBonItem = await _context.KassaBonItems
                           .Include(k => k.Boodschap)
                           .Include(k => k.KassaBon)
                           .AsNoTracking()
                           .Where(k => k.KassaBonId == id)
                           .OrderByDescending(k => k.KassaBon.BonDate)
                           .OrderBy(k => k.Id)              //Show the list as appearing on paper
                           .ToListAsync();

            PageTotalPrijs = KassaBonItem.Sum(s => s.Prijs) - KassaBonItem.Where(s => s.Korting != null).Sum(s => (decimal)s.Korting);

            if (KassaBon == null)
            {
                return(NotFound());
            }
            return(Page());
        }