Datatable linq 用法

1. using System;
   using System.Collections.Generic;
   using System.Linq;
   using System.Web;
   using System.Web.UI;
   using System.Web.UI.WebControls;
   using System.Data;
   namespace WebApplication_study.Linq
   {
   public partial class LinqStart : System.Web.UI.Page
   {
   protected void Page_Load(object sender, EventArgs e)
   {
   DataTable dt = getDataTable.getData();//源数据
   //Linq进行普通查询
   var q1 = from dt1 in dt.AsEnumerable()//查询
   orderby dt1.Field<int>("ID") descending//排序
   where dt1.Field<int>("ID") > 2 && dt1.Field<int>("ID") < 6//条件
   select dt1;
   Response.Write("查询结果为：<br/>");
   foreach (var item in q1)//显示查询结果
   {
   //Response.Write("<br/>" + item.Field<string>("Name"));//两种写法均可
   Response.Write("<br/>" + item["Name"]);
   }
   //查询结果用于新的DT
   DataTable newDT = q1.CopyToDataTable<DataRow>();//经查询生成的DT可用于数据绑定
   Response.Write("<br/><br/>新的DT的结果为：<br/>");
   foreach (var item2 in newDT.AsEnumerable())//显示查询结果
   {
   Response.Write("<br/>" + item2["Name"]);
   }
   // 修改查询的结果
   Response.Write("<br/>修改查询结果前：<br/>");
   var q3 = from dt3 in dt.AsEnumerable()
   select dt3;
   foreach (var item in q3)
   {
   Response.Write("<br/>" + item["ID"] + "&nbsp;&nbsp;&nbsp;" + item["Name"] + "&nbsp;&nbsp;&nbsp;" + item["PID"] + "&nbsp;&nbsp;&nbsp;");
   }
   Response.Write("<br/>修改查询结果后：<br/>");
   foreach (var items in dt.AsEnumerable())
   {
   int PID = (int)items["PID"];
   items.SetField<int>("PID", PID + 100);
   }
   foreach (var item in q3)
   {
   Response.Write("<br/>" + item["ID"] + "&nbsp;&nbsp;&nbsp;" + item["Name"] + "&nbsp;&nbsp;&nbsp;" + item["PID"] + "&nbsp;&nbsp;&nbsp;");
   }
   //DataView测试
   DataView dvDT = dt.AsDataView();
   EnumerableRowCollection<DataRow> quert4 = from dv in dt.AsEnumerable() select dv;
   DataView dvDTQ = quert4.AsDataView();
   
   //linq调用本地方法
   //定义本地方法
   Response.Write("<br/>linq调用本地方法：<br/>");
   int[] num = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
   var query = from i in num where check(i) select i;
   foreach (var item in query)
   {
   Response.Write(item + " ");
   }
   }
   /// <summary>
   /// 本地方法示例
   /// </summary>
   /// <param name="num"></param>
   /// <returns></returns>
   public bool check(int num)
   {
   if (num > 5)
   return true;
   else
   return false;
   }
   }
   }

转载于:https://www.cnblogs.com/kainjie/p/4553856.html