ASP Sorting

Index.cs

// Pages.Student.Index.cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.RazorPages;
using Microsoft.EntityFrameworkCore;
using ContosoUniversity.Data;
using ContosoUniversity.Models;

namespace ContosoUniversity.Pages.Students
{
    public class IndexModel : PageModel
    {
        private readonly SchoolContext _context;
        public IndexModel(SchoolContext context)
        {
            _context = context;
        }

        public string NameSort { get; set; }
        public string DateSort { get; set; }
        public string CurrentFilter { get; set; }
        public string CurrentSort { get; set; }

        public IList<Student> Students { get; set; }

        public async Task OnGetAsync(string sortOrder)
        {
            // using System;
            NameSort = String.IsNullOrEmpty(sortOrder) ? "name_desc" : "";
            DateSort = sortOrder == "Date" ? "date_desc" : "Date";

            IQueryable<Student> studentsIQ = from s in _context.Students
                                             select s;

            switch (sortOrder)
            {
                case "name_desc":
                    studentsIQ = studentsIQ.OrderByDescending(s => s.LastName);
                    break;
                case "Date":
                    studentsIQ = studentsIQ.OrderBy(s => s.EnrollmentDate);
                    break;
                case "date_desc":
                    studentsIQ = studentsIQ.OrderByDescending(s => s.EnrollmentDate);
                    break;
                default:
                    studentsIQ = studentsIQ.OrderBy(s => s.LastName);
                    break;
            }

            Students = await studentsIQ.AsNoTracking().ToListAsync();
        }
    }
}
// Page.Student.Index.cshtml

@page
@model ContosoUniversity.Pages.Students.IndexModel

@{
    ViewData["Title"] = "Students";
}

<h2>Students</h2>
<p>
    <a asp-page="Create">Create New</a>
</p>

<table class="table">
    <thead>
        <tr>
            <th>
                <a asp-page="./Index" asp-route-sortOrder="@Model.NameSort">
                    @Html.DisplayNameFor(model => model.Students[0].LastName)
                </a>
            </th>
            <th>
                @Html.DisplayNameFor(model => model.Students[0].FirstMidName)
            </th>
            <th>
                <a asp-page="./Index" asp-route-sortOrder="@Model.DateSort">
                    @Html.DisplayNameFor(model => model.Students[0].EnrollmentDate)
                </a>
            </th>
            <th></th>
        </tr>
    </thead>
    <tbody>
        @foreach (var item in Model.Students)
        {
            <tr>
                <td>
                    @Html.DisplayFor(modelItem => item.LastName)
                </td>
                <td>
                    @Html.DisplayFor(modelItem => item.FirstMidName)
                </td>
                <td>
                    @Html.DisplayFor(modelItem => item.EnrollmentDate)
                </td>
                <td>
                    <a asp-page="./Edit" asp-route-id="@item.ID">Edit</a> |
                    <a asp-page="./Details" asp-route-id="@item.ID">Details</a> |
                    <a asp-page="./Delete" asp-route-id="@item.ID">Delete</a>
                </td>
            </tr>
        }
    </tbody>
</table>

/*
The preceding code:

    Requires adding using System;.
    Adds properties to contain the sorting parameters.
    Changes the name of the Student property to Students.
    Replaces the code in the OnGetAsync method.

The OnGetAsync method receives a sortOrder parameter from the query string in the URL. The URL and query string is generated by the Anchor Tag Helper.

The sortOrder parameter is either Name or Date. The sortOrder parameter is optionally followed by _desc to specify descending order. The default sort order is ascending.

When the Index page is requested from the Students link, there's no query string. The students are displayed in ascending order by last name. Ascending order by last name is the default in the switch statement. When the user clicks a column heading link, the appropriate sortOrder value is provided in the query string value.

NameSort and DateSort are used by the Razor Page to configure the column heading hyperlinks with the appropriate query string values:
*/