Asp.net 核心分页不适用于数据表存储过程

Question

I get this error:

An unhandled exception occurred while processing the request.
NotImplementedException: The method or operation is not implemented.
Portal.Models.PaginatedList.CreateAsync(object p, int v, int pageSize) in PaginatedList.cs, line 47

Controller:

public async Task<IActionResult> Index(string sortOrder,
                                       string currentFilter,
                                       string searchString,
                                       int? pageNumber)
{
    List<StudentViewModal> listOfStudents = new List<StudentViewModal>();

    DataTable dataTable = new DataTable();

    using (SqlConnection sqlConnection = new SqlConnection(_configuration.GetConnectionString("SCHOOL")))
    {
        sqlConnection.Open();

        SqlDataAdapter sqlDa = new SqlDataAdapter("proc_GetStudents", sqlConnection);
        sqlDa.SelectCommand.CommandType = CommandType.StoredProcedure;
        sqlDa.Fill(dataTable);

        foreach (DataRow dr in dataTable.Rows)
        {
            listOfStudents.Add(
                new StudentViewModal
                {
                    ID = Convert.ToInt32(dr["ID"]),
                    Name = Convert.ToString(dr["Name"]),
                });
        }
    }

    int pageSize = 3;

    return View(await PaginatedList<StudentViewModal>.CreateAsync(listOfStudents, pageNumber ?? 1, pageSize));
}

Here is the pagination helper class:

namespace Portal.Models.Referral
{
    public class PaginatedList<T> : List<T>
    {
        public int PageIndex { get; private set; }
        public int TotalPages { get; private set; }

        public PaginatedList(List<T> items, int count, int pageIndex, int pageSize)
        {
            PageIndex = pageIndex;
            TotalPages = (int)Math.Ceiling(count / (double)pageSize);

            this.AddRange(items);
        }

        public bool HasPreviousPage
        {
            get
            {
                return (PageIndex > 1);
            }
        }

        public bool HasNextPage
        {
            get
            {
                return (PageIndex < TotalPages);
            }
        }

        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);
        }

        internal static Task<object> CreateAsync(object p, int v, int pageSize)
        {
            throw new NotImplementedException();
        }
    }
}

Answer 1

internal static Task<object> CreateAsync(object p, int v, int pageSize)

Is being called instead of

public static async Task<PaginatedList<T>> CreateAsync(IQueryable<T> source, int pageIndex, int pageSize)

because every parameter matches "object p" including parameters of type IQueryable

You have to make parameter p more specific or actually implement that method.

More Detail:

Here's what's causing your problem:

 throw new NotImplementedException();

If you implement (write the actual functional code) your error will go away.

But why is it getting top that point in the code (Line 47)

The reason is that List listOfStudents is also an object type because everything in C# extends object. So that means that

CreateAsync(listOfStudents, pageNumber ?? 1, pageSize)

matches the signature of

 internal static Task<object> CreateAsync(object p, int v, int pageSize)
    {
        throw new NotImplementedException();
    }

and it gets called and throws the NotImplementedException.

Answer 2

Asp.net core pagination works with Entity framework to query database and only return certain data. since running stored procedure return all of data then pagination is no longer useful as all data that is probably not required is already arrived. one of the reasons we do pagination is to reduce the time and not get extra data that is not needed now. if we like to do pagination in view then we can use a JavaScript library. otherwise pagination needs to be done inside stored procedure, or if we want Asp.net core to do pagination for us then we need to switch to Entity framework and use LINQ queries inside C#.