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

            Sale = await _context.Sale
                   .Include(s => s.Product)
                   .Include(s => s.SalesAgent).FirstOrDefaultAsync(m => m.Id == id);

            if (Sale == null)
            {
                return(NotFound());
            }
            ViewData["ProductId"]    = new SelectList(_context.Product, "Id", "Name");
            ViewData["SalesAgentId"] = new SelectList(_context.Set <SalesAgent>(), "Id", "AgentName");
            return(Page());
        }
 public IActionResult OnGet()
 {
     ViewData["ProductId"]    = new SelectList(_context.Product, "Id", "Name");
     ViewData["SalesAgentId"] = new SelectList(_context.Set <SalesAgent>(), "Id", "AgentName");
     return(Page());
 }