要实现Ext Grid的远程排序其实很简单，只要修改查询语句的排序关键字就可以了，但是，如果你的项目是使用Linq进行开发的，会发现动态修改排序关键字并不是那么容易的事，解决办法就是使用LINQ Dynamic Query Library。LINQ Dynamic Query Library是一个很实用很强大的库函数，通过该库，可以轻松实现一些需要通过动态参数实现的Linq查询。
本文将通过一个实例演示如何使用LINQ Dynamic Query Library实现Ext Grid的远程排序。LINQ Dynamic Query Library可以在VS2008的例程里找到，也可以从以下链接下载：
VB Dynamic Query Library (included in the /Language Samples/LINQ Samples/DynamicQuery directory)
C# Dynamic Query Library (included in the /LinqSamples/DynamicQuery directory)
本例子将使用SQL Server的“NORTHWND”样例数据库。Ext Grid显示的是Employees表的数据。以下是客户端的完整代码：
<html> <head> <title></title> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" xmlns="" /> <link rel="stylesheet" type="text/css" href="lib/ext/resources/css/ext-all.css" /> <link rel="stylesheet" type="text/css" href="css/application.css" /> </head> <script type="text/javascript" src="lib/ext/ext-base.js"></script> <script type="text/javascript" src="lib/ext/ext-all.js"></script> <script type="text/javascript" src="lib/ext/locale/ext-lang-zh_CN.js"></script> <body scroll="no"> <div id="loading-mask"></div> <div id="loading"> <div class="loading-indicator"><img alt="" src="lib/ext/resources/images/default/shared/large-loading.gif" width="32" height="32" align="absmiddle"/>正在加载...</div> </div> <script type="text/javascript"> var app={} Ext.onReady(function(){ Ext.BLANK_IMAGE_URL='lib/ext/resources/images/default/s.gif'; Ext.QuickTips.init(); Ext.form.Field.prototype.msgTarget = 'side'; Ext.Msg.minWidth=300; app.store=new Ext.data.Store({ url:'employees_action.ashx?act=list', baseParams:{}, reader:new Ext.data.JsonReader({ totalProperty: "results", root:"rows", id:"id" },[{name: 'id',type:'int'},{name:'lastname'},{name:'firstname'}, {name:'title'},{name:'titleofcourtesy'},{name:'city'}, {name:'address'},{name:'region'},{name:'postalcode'},{name:'homephone'},{name:'country'}, {name:'birthdate',type: 'date',dateFormat:'Y-m-d'}, {name:'hiredate',type: 'date',dateFormat:'Y-m-d'} ]), remoteSort: true }) //store app.pageToolbar=new Ext.PagingToolbar({ pageSize:3,displayInfo:true,store:app.store }); app.grid=new Ext.grid.GridPanel({layout:'fit', store:app.store, autoExpandColumn:2,tbar:app.pageToolbar, columns: [ {id:'id',header: "ID",width:80,dataIndex:'id',sortable: true}, {header: "FirstName",width:80, dataIndex:'firstname',sortable: true}, {header: "LastName",width:80, dataIndex:'lastname',sortable: true}, {header: "Title",width:80, dataIndex:'title',sortable: true}, {header: "Title of Courtesy",width:80, dataIndex:'titleofcourtesy',sortable: true}, {header: "City",width:80, dataIndex:'city',sortable: true}, {header: "Region",width:80, dataIndex:'region',sortable: true}, {header: "Country",width:80, dataIndex:'country',sortable: true}, {header: "Postalcode",width:80, dataIndex:'postalcode',sortable: true}, {header: "Homephone",width:80, dataIndex:'homephone',sortable: true}, {header: "Birthdate", width: 120,dataIndex:'birthdate',sortable: true,renderer:Ext.util.Format.dateRenderer('Y-m-d')}, {header: "Hiredate", width: 120,dataIndex:'hiredate',sortable: true,renderer:Ext.util.Format.dateRenderer('Y-m-d')} ] }) var viewport = new Ext.Viewport({layout:'fit',items:[app.grid]}); app.store.load(); setTimeout(function(){ Ext.get('loading').remove(); Ext.get('loading-mask').fadeOut({remove:true}); }, 250); })//onReady </script> </body> </html>代码很简单，定义了一个Store、PagetoolBar和Grid。因为Employees表数据只有9条，所以设置了每页3条数据。在Store定义中将remoteSort设置为true，说明数据要实现远程排序。Grid的每一列都将sortable属性设置为true，说明都可以通过单击Grid的列标题实现排序。
以下是服务器端的完整代码：
<%@ WebHandler Language="C#" Class="employees_action" Debug="true" %> using System; using System.Web; using System.Linq; using System.Linq.Dynamic; using System.Collections; using System.Collections.Generic; using System.Web.Security; using LitJson; public class employees_action : IHttpHandler { public void Proce***equest (HttpContext context) { string action = context.Request.Params["act"]; string outputStr = ""; if (action == null) action = ""; switch (action.ToLower()) { case "list": outputStr = List(context); break; default: outputStr = HDQ.Functions.WriteJsonResult(false, "错误的操作类型！"); break; } context.Response.ContentType = "text/javascript"; context.Response.Write(outputStr); } public bool IsReusable { get { return false; } } private string List(HttpContext context) { int limit=0; int.TryParse(context.Request.Params["limit"], out limit); if (limit == 0) limit = 3; int start=0; int.TryParse(context.Request.Params["start"], out start); string orderColumn = context.Request.Params["sort"]; string orderBy = context.Request.Params["dir"] == "ASC" ? "" : "descending"; switch (orderColumn) { case "id": orderColumn = "EmployeeID"; break; case "lastname": orderColumn = "LastName"; break; case "firstname": orderColumn = "FirstName"; break; case "title": orderColumn = "Title"; break; case "titleofcourtesy": orderColumn = "TitleOfCourtesy"; break; case "birthdate": orderColumn = "BirthDate"; break; case "hiredate": orderColumn = "HireDate"; break; case "address": orderColumn = "Address"; break; case "city": orderColumn = "City"; break; case "region": orderColumn = "Region"; break; case "postalcode": orderColumn = "PostalCode"; break; case "country": orderColumn = "Country"; break; case "homephone": orderColumn = "HomePhone"; break; default: orderColumn = "EmployeeID"; break; } DBDemosDataContext dc = new DBDemosDataContext(); int recordCount=0; JsonWriter jw = new JsonWriter(); jw.WriteObjectStart(); jw.WritePropertyName("rows"); jw.WriteArrayStart(); recordCount = dc.Employees.Count(); if (start > recordCount) start = 0; var q=dc.Employees.OrderBy(orderColumn + " " + orderBy).Skip(start).Take(limit); foreach (var c in q) { jw.WriteObjectStart(); jw.WritePropertyName("id"); jw.Write(c.EmployeeID); jw.WritePropertyName("firstname"); jw.Write(c.FirstName); jw.WritePropertyName("lastname"); jw.Write(c.LastName); jw.WritePropertyName("title"); jw.Write(c.Title); jw.WritePropertyName("titleofcourtesy"); jw.Write(c.TitleOfCourtesy); jw.WritePropertyName("address"); jw.Write(c.Address); jw.WritePropertyName("city"); jw.Write(c.City); jw.WritePropertyName("region"); jw.Write(c.Region); jw.WritePropertyName("country"); jw.Write(c.Country); jw.WritePropertyName("postalcode"); jw.Write(c.PostalCode); jw.WritePropertyName("homephone"); jw.Write(c.HomePhone); jw.WritePropertyName("birthdate"); jw.Write(c.BirthDate == null ? "" : Convert.ToDateTime(c.BirthDate).ToString("yyyy-MM-dd")); jw.WritePropertyName("hiredate"); jw.Write(c.HireDate == null ? "" : Convert.ToDateTime(c.HireDate).ToString("yyyy-MM-dd")); jw.WriteObjectEnd(); } jw.WriteArrayEnd(); jw.WritePropertyName("results"); jw.Write(recordCount.ToString()); jw.WriteObjectEnd(); return jw.ToString(); } }代码中Proce***equest方法根据提交的参数action执行对应的方法。本文主要是执行List方法。
在List方法的开头首先获取了客户端提交的几个参数，参数对应的说明请看下表：
| 参数 | 说明 |
| limit | 每页总数，本例子是3 |
| start | 提取数据开始位置 |
| sort | 要排序的列 |
| dir | 排序顺序 |
获取数据后需要对排序的列名和顺序做一下转换，以下语句就是实现排序顺序的转换：
| string orderBy = context.Request.Params["dir"] == "ASC" ? "" : "descending"; |
列名的转换则通过switch语句实现。如果在客户端定义的列名与数据库的真实列名相同，也可以不实施转换。不过，出于安全考虑，建议无论如何，还是要实行转换。转换完成后，就可以定义查询语句了，相当的简单：
| var q=dc.Employees.OrderBy(orderColumn + " " + orderBy).Skip(start).Take(limit); |
将列名变量和顺序变量组合成字符串作为OrderBy方法的参数就可以了。LINQ Dynamic Query Library会自动重新生成Linq语句执行。后面的代码就是将查询结果组合成Json格式数据输出。 如果不使用LINQ Dynamic Query Library，远程排序的实现最直接的方法就是使用switch语句，根据提交的列和排序顺序写不同的Linq语句，就不如本例的代码那么简洁了。
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