ASP.NET Core 2.0 Paging help needed

Question

Needed help again. So I am currently working on ASP.NET Core 2.0 Paging and it's not working properly.

I followed the tutorial here https://learn.microsoft.com/en-us/aspnet/core/data/ef-mvc/sort-filter-page

However, the thing is that the tutorial is using Entity Framework dateset or IQuery? I however is using List<>. Does anyone know how to solve this problem or convert my List into EF DataSet or something?

Controller Paginated.cs :

public static async Task<PaginatedList<T>> CreateAsync(IQueryable<T> source, int pageIndex, int pageSize)
{
    var count = await source.CountAsync();
    var items = await source.Skip((pageIndex - 1) * pageSize).Take(pageSize).ToListAsync();
    return new PaginatedList<T>(items, count, pageIndex, pageSize);
}

Controller:

public async Task<IActionResult> Index(string sortOrder, string currentFilter, string searchString, int? page)
{
    ViewData["CurrentSort"] = sortOrder;
    ViewBag.CurrentSort = sortOrder;
    var students = addList();

    ViewData["NameSortParm"] = String.IsNullOrEmpty(sortOrder) ? "name_desc" : "";
    if (searchString != null)
    {
        page = 1;
    }
    else
    {
        searchString = currentFilter;
    }

    ViewBag.CurrentFilter = searchString;


    switch (sortOrder)
    {
        case "name_desc":
            students = students.OrderByDescending(s => s.Name).ToList();
            break;
        default:
            break;
    }

    if (searchString != null)
    {
        page = 1;
    }
    else
    {
        searchString = currentFilter;
    }

    ViewData["CurrentFilter"] = searchString;
    int pageSize = 3;
    return View(await PaginatedList<Student>.CreateAsync(students.AsNoTracking(), page ?? 1, pageSize));
    // return View(PaginatedList<Student>(students, page ?? 1, pageSize));
}

If you look at the code above, it only works if it is dataset retrieve from EF.

The CountAsync(), students.AsNoTracking() is not working because it is a List.

Anyone know what should I do? Let me know if you need anything.

Thanks!

EDit:

public IQueryable<Student> addList()
{
    var studentList = new List<Student>();
    studentList.Add(new Student
    {
        Id = 1,
        Name = "David",
        ClassName = "Moria"
    });

    studentList.Add(new Student
    {
        Id = 2,
        Name = "Jenny",
        ClassName = "Moria"
    });

    studentList.Add(new Student
    {
        Id = 3,
        Name = "Crystal",
        ClassName = "Moria"
    });

    studentList.Add(new Student
    {
        Id = 4,
        Name = "jenny",
        ClassName = "Moria"
    });

    studentList.Add(new Student
    {
        Id = 5,
        Name = "Andria",
        ClassName = "Moria"
    });

    studentList.Add(new Student
    {
        Id = 6,
        Name = "Sweet",
        ClassName = "Moria"
    });

    studentList.Add(new Student
    {
        Id = 7,
        Name = "Susan",
        ClassName = "Moria"
    });
    return studentList.AsQueryable();
}

Answer 1

Your addList() is just creating an in-memory set of hard coded data. There is no point using async methods (and it is actually degrading performance) or using IQueryable (your not querying an external data source).

I suggest rename your addlist method to something more meaningful, say FetchStudents(). Since your generating List<Student> in the method, it should return IList<Student>

public IList<Student> FetchStudents()
{
    ....
    return studentList;
}

Next change the CreateAsync() method to accept IEnumerable<T> and remove the async calls

public static PaginatedList<T> Create(IEnumerable<T> source, int pageIndex, int pageSize)
{
    var count = source.Count();
    var items = source.Skip((pageIndex - 1) * pageSize).Take(pageSize).ToList();
    return new PaginatedList<T>(items, count, pageIndex, pageSize);
}

and finally modify the Index() method to

public IActionResult Index(string sortOrder, string currentFilter, string searchString, int? page)
{
    ....
    var students = FetchStudents();
    ....
    return View(PaginatedList<Student>.Create(students, page ?? 1, pageSize));
}