Datatable linq 用法
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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"] + " " + item["Name"] + " " + item["PID"] + " ");
}
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"] + " " + item["Name"] + " " + item["PID"] + " ");
}
//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;
}
}
}
