原文：Sorting, Filtering, and Paging with the Entity Framework in an ASP.NET MVC Application
1.添加排序：
1.1.修改Controllers\StudentController.cs的Index：
public ActionResult Index(string sortOrder)
{
ViewBag.NameSortParm = String.IsNullOrEmpty(sortOrder) ? "name_desc" : "";
ViewBag.DateSortParm = sortOrder == "Date" ? "date_desc" : "Date";
var students = from s in db.Students
select s;
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;
}
return View(students.ToList());
}
1.2.修改Views\Student\Index.cshtml：
<p>
@Html.ActionLink("Create New", "Create")
</p>
<table>
<tr>
<th>
@Html.ActionLink("Last Name", "Index", new { sortOrder = ViewBag.NameSortParm })
</th>
<th>First Name
</th>
<th>
@Html.ActionLink("Enrollment Date", "Index", new { sortOrder = ViewBag.DateSortParm })
</th>
<th></th>
</tr>
效果图：
2.添加搜索框：
2.1.修改Controllers\StudentController.cs的Index：
public ViewResult Index(string sortOrder, string searchString)
{
ViewBag.NameSortParm = String.IsNullOrEmpty(sortOrder) ? "name_desc" : "";
ViewBag.DateSortParm = sortOrder == "Date" ? "date_desc" : "Date";
var students = from s in db.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;
}
return View(students.ToList());
}
在大多数情况下，我们调用同一个方法时，在EF实体集和内存中集合的扩展方法返回的结果是一样的;但是在一些情况下返回结果会不一样。
例如当传递一个空的字符串时.NET Framework的Contains方法返回所有行，但是SQL Server Compact 4.0的EF 提供者（provider）的Contains返回0行。因此上面的代码中把Where语句放在if语句中，以保证对所有的SQL Server版本返回相同的数据。同样，.NET Framework的Contains方法默认是区分大小写的，因此，使用ToUpper方法将字符串显示转换为大写以确保以后代码改为仓储时（返回类型由IQueryable类型变成IEnumerable类型）返回结果不会发生变化（当调用Contains方法返回IEnumerable集合时，调用的是.NET Framework实现；返回IQueryable对象时，调用的是数据库提供者的实现）。
当我们返回IQueryable对象时，不同的数据库提供者对空值的处理也不同。例如，在有些脚本中where条件中的table.Column != 0可能不会返回空值列。
2.2.为Views\Student\Index.cshtml添加搜索框：
<p>
@Html.ActionLink("Create New", "Create")
</p>
@using (Html.BeginForm())
{
<p>
Find by name: @Html.TextBox("SearchString")
<input type="submit" value="Search" />
</p>
}
效果图：
3.添加分页：
3.1.安装PagedList.MVC：
Install-Package PagedList.Mvc
3.2.修改Controllers\StudentController.cs：
using PagedList;
public ViewResult Index(string sortOrder, string currentFilter, string searchString, int? page)
{
ViewBag.CurrentSort = sortOrder;
ViewBag.NameSortParm = String.IsNullOrEmpty(sortOrder) ? "name_desc" : "";
ViewBag.DateSortParm = sortOrder == "Date" ? "date_desc" : "Date";
if (searchString != null)
{
page = 1;
}
else
{
searchString = currentFilter;
}
ViewBag.CurrentFilter = searchString;
var students = from s in db.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: // Name ascending
students = students.OrderBy(s => s.LastName);
break;
}
int pageSize = 3;
int pageNumber = (page ?? 1);
return View(students.ToPagedList(pageNumber, pageSize));
}
当页面第一次加载或者用户没有点击分页或排序链接时，所有的参数都是空值。
ViewBag.CurrentSort用于点击分页时保存排序信息。
ViewBag.CurrentFilter用于保存搜索信息，并且当页面刷新时给搜索框赋值。当搜索条件改变时，page值重置为1。
3.3.修改Views\Student\Index.cshtml：
@model PagedList.IPagedList<ContosoUniversity.Models.Student>
@using PagedList.Mvc;
<link href="~/Content/PagedList.css" rel="stylesheet" type="text/css" />
@{
ViewBag.Title = "Students";
}
<h2>Students</h2>
<p>
@Html.ActionLink("Create New", "Create")
</p>
@using (Html.BeginForm("Index", "Student", FormMethod.Get))
{
<p>
Find by name: @Html.TextBox("SearchString", ViewBag.CurrentFilter as string)
<input type="submit" value="Search" />
</p>
}
<table class="table">
<tr>
<th>
@Html.ActionLink("Last Name", "Index", new { sortOrder = ViewBag.NameSortParm, currentFilter=ViewBag.CurrentFilter })
</th>
<th>
First Name
</th>
<th>
@Html.ActionLink("Enrollment Date", "Index", new { sortOrder = ViewBag.DateSortParm, currentFilter=ViewBag.CurrentFilter })
</th>
<th></th>
</tr>
@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>
@Html.ActionLink("Edit", "Edit", new { id=item.ID }) |
@Html.ActionLink("Details", "Details", new { id=item.ID }) |
@Html.ActionLink("Delete", "Delete", new { id=item.ID })
</td>
</tr>
}
</table>
<br />
Page @(Model.PageCount < Model.PageNumber ? 0 : Model.PageNumber) of @Model.PageCount
@Html.PagedListPager(Model, page => Url.Action("Index",
new { page, sortOrder = ViewBag.CurrentSort, currentFilter = ViewBag.CurrentFilter }))
BeginForm提交form数据的默认方式是post，post方式是通过HTTP消息体而不是通过URL查询字符串传递参数。我们通过FormMethod.Get把它指定为HTTP GET,这样用户就可以将URL收藏为书签。当动作不会导致更新时W3C HTTP GET使用指南推荐我们使用GET。
效果图：
4.添加About页面展示Student统计信息：
4.1.创建视图模型：
新建ViewModels文件夹EnrollmentDateGroup.cs：
public class EnrollmentDateGroup
{
[DataType(DataType.Date)]
public DateTime? EnrollmentDate { get; set; }
public int StudentCount { get; set; }
}
4.2.修改HomeController.cs：
private SchoolContext db = new SchoolContext();
//...
public ActionResult About()
{
IQueryable<EnrollmentDateGroup> data = from student in db.Students
group student by student.EnrollmentDate into dateGroup
select new EnrollmentDateGroup()
{
EnrollmentDate = dateGroup.Key,
StudentCount = dateGroup.Count()
};
return View(data.ToList());
}
//...
protected override void Dispose(bool disposing)
{
db.Dispose();
base.Dispose(disposing);
}
4.3.修改Views\Home\About.cshtml：
@model IEnumerable<ContosoUniversity.ViewModels.EnrollmentDateGroup>
@{
ViewBag.Title = "Student Body Statistics";
}
<h2>Student Body Statistics</h2>
<table>
<tr>
<th>
Enrollment Date
</th>
<th>
Students
</th>
</tr>
@foreach (var item in Model) {
<tr>
<td>
@Html.DisplayFor(modelItem => item.EnrollmentDate)
</td>
<td>
@item.StudentCount
</td>
</tr>
}
</table>
效果图：
时间： 2024-10-10 06:35:09