在开发Web应用程序时，分页是一个常见且重要的需求。本文将介绍如何在不使用第三方库的情况下，实现一个可复用、可定制的分页功能。
在探索了众多教程和库之后，发现了一个功能齐全的库，但它在查询时会锁定数据库，这并不适合。因此，对分页功能的要求如下：
假设正在开发一个人员信息的Web应用程序。使用SQL Server创建了一个名为“Person”的表：
IF NOT EXISTS (
SELECT 1 FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME = 'Person' AND TABLE_SCHEMA = 'dbo'
) BEGIN
CREATE TABLE dbo.Person (
ID INT IDENTITY(1,1) NOT NULL PRIMARY KEY,
CreateDate DATETIME NOT NULL DEFAULT GETDATE(),
Creator VARCHAR(100) NOT NULL,
ModifyDate DATETIME NULL,
Modifier VARCHAR(20) NULL,
FirstName VARCHAR(150) NOT NULL,
LastName VARCHAR(1000) NOT NULL
) ON [PRIMARY]
END
GO
使用了Entity Framework的DatabaseFirst方法，生成了以下类：
public partial class Person
{
public int ID { get; set; }
public System.DateTime CreateDate { get; set; }
public string Creator { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public Nullable ModifyDate { get; set; }
public string Modifier { get; set; }
}
接下来，定义视图模型类，包含数据和分页信息：
public class DataResultViewModel<T>
{
public IEnumerable<T> Items { get; set; }
public Pagination Pagination { get; set; }
}
public class PersonViewModel
{
public int ID { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
}
public class RouteInfo
{
public string ControllerName { get; set; }
public string ActionName { get; set; }
}
public class Pagination
{
public int TotalItems { get; set; }
public int PageSize { get; set; } = 5;
public int Page { get; set; }
public string SortBy { get; set; }
public bool IsSortAscending { get; set; }
public RouteInfo RouteInfo { get; set; }
}
然后，定义一个扩展方法类，用于实现分页：
public static class IQueryableExtension
{
public static IQueryable<T> UseOrdering<T, TResultSelector>(this IQueryable<T> query, Pagination pagination, Expression<Func<T, TResultSelector>> field)
{
if (string.IsNullOrWhiteSpace(pagination.SortBy) || string.IsNullOrEmpty(pagination.SortBy))
return query;
return pagination.IsSortAscending ? query.OrderBy(field) : query.OrderByDescending(field);
}
public static IQueryable<T> UsePagination<T>(this IQueryable<T> query, Pagination pagination)
{
if (pagination.Page <= 0) pagination.Page = 1;
if (pagination.PageSize <= 0) pagination.PageSize = 10;
return query.Skip((pagination.Page - 1) * pagination.PageSize).Take(pagination.PageSize);
}
}
接下来是服务层的实现：
public class PersonService
{
public DataResultViewModel<PersonViewModel> GetWithPagination(Pagination pagination, Expression<Func<Person, DateTime>> fieldName)
{
var result = new DataResultViewModel<PersonViewModel>();
using (var db = new MiscellaneousEntities())
{
var persons = db.Person.AsQueryable();
result.Pagination = pagination;
result.Pagination.TotalItems = persons.Count();
result.Pagination.RouteInfo = new RouteInfo() { ActionName = "Index", ControllerName = "Person" };
if (pagination.SortBy == null) pagination.SortBy = "CreateDate";
persons = persons.UseOrdering(pagination, fieldName);
persons = persons.UsePagination(pagination);
result.Items = persons.Select(s => new PersonViewModel { ID = s.ID, FirstName = s.FirstName, LastName = s.LastName }).ToList();
return result;
}
}
}
最后是控制器的实现：
public class PersonController : Controller
{
PersonService _personService;
public PersonController()
{
_personService = new PersonService();
}
public ActionResult Index(int? page, int? pageSize, string sortBy, bool? isSortAscending)
{
return View(_personService.GetWithPagination(new Pagination
{
Page = page ?? 1,
PageSize = pageSize ?? 3,
SortBy = sortBy,
IsSortAscending = isSortAscending ?? false
}, v => v.CreateDate));
}
}
接下来，需要创建视图。这是一个需要分页的人员视图：
@model OnlyPagination.ViewModel.DataResultViewModel<OnlyPagination.ViewModel.PersonViewModel>
<div class="d-flex justify-content-center">
<div>
@foreach (var item in Model.Items)
{
<div>
<p>Id is @item.ID</p>
<p>FirstName is @item.FirstName</p>
<p>LastName is @item.LastName</p>
</div>
<hr />
}
</div>
</div>
<div class="d-flex justify-content-center">
@{
@Html.Partial("Pagination", Model.Pagination)
}
</div>
这是一个可复用的分页部分视图：
@model OnlyPagination.Extensions.Query.Model.Pagination
@{
var pagesCount = Math.Ceiling((decimal)Model.TotalItems / (decimal)Model.PageSize);
var pages = new List<int>();
for (var i = 1; i <= pagesCount; i++)
{
pages.Add(i);
}
}
<div>
<p class="d-flex justify-content-center">
Page @Model.Page of @pagesCount
</p>
<ul class="pagination">
<li class="page-item @(Model.Page == 1 ? "disabled" : "")">
<a aria-label="Previous" class="page-link" href="@Url.Action(Model.RouteInfo.ActionName, Model.RouteInfo.ControllerName, new { page = Model.Page - 1, pageSize = Model.PageSize })">
<span aria-hidden="true">«</span>
</a>
</li>
@for (int pageNumber = 1; pageNumber <= pages.Count; pageNumber++)
{
<li class="page-item @(Model.Page == pageNumber ? "active" : "")">
<a class="page-link" href="@Url.Action(Model.RouteInfo.ActionName, Model.RouteInfo.ControllerName, new { page = pageNumber, pageSize = Model.PageSize })">
@pageNumber
</a>
</li>
}
<li class="page-item @(Model.Page == pages.Count ? "disabled" : "")">
<a aria-label="Next" class="page-link" href="@Url.Action(Model.RouteInfo.ActionName, Model.RouteInfo.ControllerName, new { page = Model.Page + 1, pageSize = Model.PageSize })">
<span aria-hidden="true">»</span>
</a>
</li>
</ul>
</div>