.NETCORE linq 分页 .net分页查询

在项目文件夹中，创建 PaginatedList类，然后用以下代码替换模板代码。

 

using Microsoft.EntityFrameworkCore;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace FineUICore.Examples
{
    public class PaginatedList<T> : List<T>
    {
        public int PageIndex { get; private set; }//当前页
        public int TotalPages { get; private set; }//总页数

        public PaginatedList(List<T> items, int count, int pageIndex, int pageSize)//count：总条数 ，pageIndex：当前页，pageSize：每页显示行数
        {
            PageIndex = pageIndex;
            TotalPages = (int)Math.Ceiling(count / (double)pageSize);

            this.AddRange(items);
        }
        //判断是否为首页
        public bool HasPreviousPage
        {
            get
            {
                return (PageIndex > 1);
            }
        }
        //判断是否为尾页
        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);
        }
    }
}

 

在 StudentsController.cs 中，将 Index方法替换为以下代码。

 

public async Task<IActionResult> Index(
    string sortOrder,
    string currentFilter,
    string searchString,
    int? page)
{
    ViewData["CurrentSort"] = sortOrder;
    ViewData["NameSortParm"] = String.IsNullOrEmpty(sortOrder) ? "name_desc" : "";
    ViewData["DateSortParm"] = sortOrder == "Date" ? "date_desc" : "Date";
 
    if (searchString != null)
    {
        page = 1;
    }
    else
    {
        searchString = currentFilter;
    }
 
    ViewData["CurrentFilter"] = searchString;
 
    var students = from s in _context.Students
                   select s;
    if (!String.IsNullOrEmpty(searchString))
    {
        students = students.Where(s => s.LastName.Contains(searchString)
                               || s.FirstMidName.Contains(searchString));
    }
    switch (sortOrder)
    {
        case "name_desc":
            students = students.OrderByDescending(s => s.LastName);
            break;
        case "Date":
            students = students.OrderBy(s => s.EnrollmentDate);
            break;
        case "date_desc":
            students = students.OrderByDescending(s => s.EnrollmentDate);
            break;
        default:
            students = students.OrderBy(s => s.LastName);
            break;
    }
 
    int pageSize = 3;
    return View(await PaginatedList<Student>.CreateAsync(students.AsNoTracking(), page ?? 1, pageSize));
}

 

在 Views/Students/Index.cshtml 中，将现有代码替换为以下代码。

 

@model PaginatedList<ContosoUniversity.Models.Student>
 
@{
    ViewData["Title"] = "Index";
}
 
<h2>Index</h2>
<p>
    <a asp-action="Create">Create New</a>
</p>
 
<form asp-action="Index" method="get">
    <div class="form-actions no-color">
        <p>
            Find by name: <input type="text" name="SearchString" value="@ViewData["currentFilter"]" />
            <input type="submit" value="Search" class="btn btn-default" /> |
            <a asp-action="Index">Back to Full List</a>
        </p>
    </div>
</form>
 
<table class="table">
    <thead>
        <tr>
            <th>
                <a asp-action="Index" asp-route-sortOrder="@ViewData["NameSortParm"]" asp-route-currentFilter="@ViewData["CurrentFilter"]">Last Name</a>
            </th>
            <th>
                First Name
            </th>
            <th>
                <a asp-action="Index" asp-route-sortOrder="@ViewData["DateSortParm"]" asp-route-currentFilter="@ViewData["CurrentFilter"]">Enrollment Date</a>
            </th>
            <th></th>
        </tr>
    </thead>
    <tbody>
        @foreach (var item in Model)
        {
            <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-action="Edit" asp-route-id="@item.ID">Edit</a> |
                    <a asp-action="Details" asp-route-id="@item.ID">Details</a> |
                    <a asp-action="Delete" asp-route-id="@item.ID">Delete</a>
                </td>
            </tr>
        }
    </tbody>
</table>
 
@{
    var prevDisabled = !Model.HasPreviousPage ? "disabled" : "";
    var nextDisabled = !Model.HasNextPage ? "disabled" : "";
}
 
<a asp-action="Index"
   asp-route-sortOrder="@ViewData["CurrentSort"]"
   asp-route-page="@(Model.PageIndex - 1)"
   asp-route-currentFilter="@ViewData["CurrentFilter"]"
   class="btn btn-default @prevDisabled">
    Previous
</a>
<a asp-action="Index"
   asp-route-sortOrder="@ViewData["CurrentSort"]"
   asp-route-page="@(Model.PageIndex + 1)"
   asp-route-currentFilter="@ViewData["CurrentFilter"]"
   class="btn btn-default @nextDisabled">
    Next
</a>