(转)Linq DataTable的修改和查询

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;
        }
    }
}

PS:如果出现指定转换无效的异常，说明查询语句里面有问题。一般是Field<T>的泛型有误，应当仔细检查DataTable中列的DataType。

　　然后还可可以这么写

IEnumerable<DataRow> query =
    from order in orders.AsEnumerable()
    where order.Field<DateTime>("OrderDate") > new DateTime(2001, 8, 1)
    select order;

// Create a table from the query.
DataTable boundTable = query.CopyToDataTable<DataRow>();

本文转载自：http://www.cnblogs.com/sunxf2011/archive/2011/07/08/2101008.html