将DataSet变化保存到数据源

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;
using System.Data.SqlClient;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            SqlConnection conn = new SqlConnection("Server=zhuobin;uid=sa;pwd=zhuobin;database=Northwind");
            string sql = "select * from employees where country='UK'";
            string upd = @"update employees set city=@city where employeeid=@employeeid";
            try
            {
               //Create the DataAdapter
                SqlDataAdapter da = new SqlDataAdapter();
                da.SelectCommand = new SqlCommand(sql,conn);
                //crate the dataset and fill it
                DataSet ds = new DataSet();
                da.Fill(ds,"employees");
                //get the datatable reference
                DataTable dt=ds.Tables["employees"];
                //modify the city in the first row
                dt.Rows[0]["city"] = "Xuzhou";
                //Dislay the rows
                foreach (DataRow row in dt.Rows)
                {
                    Console.WriteLine("{0} {1} {2}",row["firstname"].ToString().PadRight(15),row["lastname"].ToString().PadLeft(25),row["city"]);

                }
                //update Employees
                SqlCommand cmd = new SqlCommand(upd,conn);
                //City 
                cmd.Parameters.Add("@city",SqlDbType.VarChar,10,"city");
                //Employees id
                SqlParameter parm = cmd.Parameters.Add("@employeeid",SqlDbType.Int,4,"employeeid");
                parm.SourceVersion = DataRowVersion.Original;
                //Update database
                da.UpdateCommand = cmd;
                da.Update(ds,"employees");

            }
            catch (SqlException ex)
            {
                Console.WriteLine("The Error:{0}", ex.Message);
            }
            finally
            {
                conn.Close();
            }
            Console.ReadLine();
        }
    }
}