Getting Unable to cast object of type 'System.Collections.Generic.List` to type 'System.Linq.IQueryable Error

Question

I've checked other posts on this, but not seeing anything similar enough to my code to clue me in enough to fix it. Please advise.

I have a report on my razor page app. Here is the .cs for it:

{
    public class IndexModel : PageModel
    {
        private readonly ApplicationDbContext _context;

        public IndexModel(ApplicationDbContext context)
        {
            _context = context;
        }

        public Attendance Attendance { get; set; }
        public Client Client { get; set; }
        public string NameSort { get; set; }
        public string CurrentSort { get; set; }
        public IEnumerable<Panel> DisplayPanelData { get; set; }
        public IEnumerable<Status> DisplayStatusData { get; set; }

        public PaginatedList<ReportModel> Registrants { get; set; } = default!;

        public async Task OnGet(string sortOrder, string panelAssigned, string attendanceStatus, int? pageIndex)
        {
            await _context.Panel.Select(a => a.PanelName).ToListAsync();
            DisplayPanelData = await _context.Panel.ToListAsync();
            await _context.Status.Select(a => a.StatusDesc).ToListAsync();
            DisplayStatusData = await _context.Status.ToListAsync();

            IQueryable<ReportModel> Registrants = (IQueryable<ReportModel>)await (from x in _context.Attendance
                                                         join y in _context.Client on x.ClientId equals y.Id
                                                        where x.PanelAssigned == panelAssigned && x.Status == attendanceStatus
                                                        select new ReportModel
                                                        {
                                                            ClientId = x.ClientId.ToString(),
                                                            ClientLastName = y.ClientLastName,
                                                            ClientFirstName = y.ClientFirstName,
                                                            ClientMI = y.ClientMI,
                                                            PanelCost = x.PanelCost,
                                                            AmountPaid = x.AmountPaid,
                                                            AmountOutstanding = x.AmountOutstanding,
                                                            Status = x.Status,
                                                        }).ToListAsync();


            CurrentSort = sortOrder;
            NameSort = string.IsNullOrEmpty(sortOrder) ? "name_desc" : "";

            switch (sortOrder)
            {
                case "name_desc":
                    Registrants = Registrants.OrderByDescending(x => x.ClientLastName).ThenByDescending(x => x.ClientFirstName);
                    break;
                default:
                    Registrants = Registrants.OrderBy(x => x.ClientLastName).ThenBy(x => x.ClientFirstName);
                    break;
            }

            int resultsPerPage = 100;
            Registrants = (IQueryable<ReportModel>)await PaginatedList<ReportModel>.CreateAsync(
                (Registrants, pageIndex ?? 1, resultsPerPage);

            ViewData["panelparameter"] = $"Panel Selected: {panelAssigned}";
            ViewData["statusparameter"] = $"Status Selected: {attendanceStatus}";
        }

    }
}

Here is the full error:

InvalidCastException: Unable to cast object of type 'System.Collections.Generic.List1[SampleApp.Model.ReportModel]' to type 'System.Linq.IQueryable1[SampleApp.Model.ReportModel]'.

When I run the app and navigate to the report page link, it errors out with this line highlighted in red:

IQueryable Registrants = (IQueryable)await (from x in _context.Attendance

Any direction would be much appreciated. Spinning my wheels. Thank you!!

Answer 1

ToListAsync() would query db at once,if you don't want to query db at once just want IQueryable<ReportModel> don't call it

Also not all types could be casted to another directly ,that's the reason for the error,you could check this document related

modify:

IQueryable<ReportModel> Registrants = (IQueryable<ReportModel>)await (from x in _context.Attendance
                                                         join y in _context.Client on x.ClientId equals y.Id
                                                        where x.PanelAssigned == panelAssigned && x.Status == attendanceStatus
                                                        select new ReportModel
                                                        {
                                                            ClientId = x.ClientId.ToString(),
                                                            ClientLastName = y.ClientLastName,
                                                            ClientFirstName = y.ClientFirstName,
                                                            ClientMI = y.ClientMI,
                                                            PanelCost = x.PanelCost,
                                                            AmountPaid = x.AmountPaid,
                                                            AmountOutstanding = x.AmountOutstanding,
                                                            Status = x.Status,
                                                        }).ToListAsync();

To

IQueryable<ReportModel> Registrants = from x in _context.Attendance
                                                         join y in _context.Client on x.ClientId equals y.Id
                                                        where x.PanelAssigned == panelAssigned && x.Status == attendanceStatus
                                                        select new ReportModel
                                                        {
                                                            ClientId = x.ClientId.ToString(),
                                                            ClientLastName = y.ClientLastName,
                                                            ClientFirstName = y.ClientFirstName,
                                                            ClientMI = y.ClientMI,
                                                            PanelCost = x.PanelCost,
                                                            AmountPaid = x.AmountPaid,
                                                            AmountOutstanding = x.AmountOutstanding,
                                                            Status = x.Status,
                                                        };