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Asp.net – InvalidCastException: Unable to cast object of type 'System.Linq.OrderedEnumerable to type 'System.Collections.Generic.List

In Asp.Net 4.8 web app, the following works. I’m using PagedList for pagination.

private AppDbContext db = new AppDbContext();
private IQueryable<Border> Broders;

public ViewResult Index(int? page)
{
    Broders = from s in db.Broders select s;

    if (SearchColumn == "T1")
    {
        Borders = Broders.Where(s => s.TagT1.ToString().Contains(searchString));
    }
    else if (SearchColumn == "T2")
    {
        Borders = Broders.Where(s => s.TagT2.ToString().Contains(searchString));
    }
    switch (sortOrder)
    {
        case "status_desc":
            Borders = Borders.OrderByDescending(s => s.Status);
            break;
        case "status_desc":
            Borders = Borders.OrderByDescending(s => s.Status);
            break;
        default:
            Borders = Borders.OrderByDescending(s => s.CreatedOn);
            break;
    }
    int pageSize = 10;
    int pageNumber = (page ?? 1);
    return View(Borders.ToPagedList(pageNumber, pageSize));
}

But when I do this in .Net 8 Asp.Net MVC Core app, I’m using X.PagedList for pagination.

private readonly AppDbContext _context;
private IQueryable<Broder> Borders;

public async Task<IActionResult> Index(int? page)
{
    var Borders = await _context.Borders.ToListAsync();
    if (SearchColumn == "T1")
    {
        Borders = (List<Initiative>)Broders.Where(s => s.TagT1.ToString().Contains(searchString));
    }
    else if (SearchColumn == "T2")
    {
        Borders = (List<Initiative>)Broders.Where(s => s.TagT2.ToString().Contains(searchString));
    }
    switch (sortOrder)
    {
        case "status_desc":
            Borders = (List<Initiative>)Borders.OrderByDescending(s => s.Status);
            break;
        case "status_desc":
            Borders = (List<Initiative>)Borders.OrderByDescending(s => s.Status);
            break;
        default:
            Borders = (List<Initiative>)Borders.OrderByDescending(s => s.CreatedOn);
            break;
    }
    int pageSize = 10;
    int pageNumber = (page ?? 1);
    return View(Borders.ToPagedList(pageNumber, pageSize));     
}

The above asp.net Core code gives me error InvalidCastException: Unable to cast object of type ‘System.Linq.OrderedEnumerable2[Map.Models.Border,System.String]' to type 'System.Collections.Generic.List1[Map.Models.Border]’ at line

Borders = (List<Initiative>)Borders.OrderByDescending(s => s.CreatedOn);

I’m new to asp.net Core, this is my first application in asp.net core. Can someone tell me what mistake am I making in my asp.net core method?

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2

Answers


  1. 0

    In your second code block you use var Borders = ... whcih defines a new variable of a different type (implied from the return of ToList and hides the page field. So just removing the var would be a start to get them in sync, but it may require other changes as well.

    For example, you may also need to remove the ToList since a list cannot be assigned to an IQueryable variable. It will also stop loading the entire Borders table in memory only to apply filters after that.

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  2. 0

    From this line:

    var Borders = await _context.Borders.ToListAsync();

    you are declaring Borders which is a List<Border> type.

    Changes:

    1. Declare the Borders as IQueryable<Border> with .AsQueryable().

    2. Remove casting to List<Initiative> which seems unnecessary.

    3. Don’t need to create variable with global scope: private IQueryable<Broder> Borders;

    public async Task<IActionResult> Index(int? page)
{
    IQueryable<Broder> Borders = _context.Borders.AsQueryable();
    if (SearchColumn == "T1")
    {
        Borders = Borders.Where(s => s.TagT1.ToString().Contains(searchString));
    }
    else if (SearchColumn == "T2")
    {
        Borders = Borders.Where(s => s.TagT2.ToString().Contains(searchString));
    }
    switch (sortOrder)
    {
        case "status_desc":
            Borders = Borders.OrderByDescending(s => s.Status);
            break;
        case "status_desc":
            Borders = Borders.OrderByDescending(s => s.Status);
            break;
        default:
            Borders = Borders.OrderByDescending(s => s.CreatedOn);
            break;
    }
    int pageSize = 10;
    int pageNumber = (page ?? 1);
    return View(Borders.ToPagedList(pageNumber, pageSize));     
}
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