SqlCommandBuilder对像来自动构建sql命令

string sConnectonString;
            sConnectonString = "Password=sa;user id = sa;Initial Catalog = master;Data Source=(local)";
            SqlConnection objConn = new SqlConnection(sConnectonString);
            objConn.Open();
                       
            SqlDataAdapter daAuthors = new SqlDataAdapter("select * from city_users", objConn);
            DataSet dsMaster = new DataSet("master");
            daAuthors.FillSchema(dsMaster, SchemaType.Source, "city_users");//加载表的构架，这样在操作加载到dataset里的表时就不用重新设置主键了
            daAuthors.Fill(dsMaster, "city_users");
            dsMaster.Tables["city_users"].Rows[1]["user_name"] = "sql";//注意这里的Rows[1]，这个1指得是在DataSet里的表里的行号，其与数据库里的行号不一致如图1
            
            SqlCommandBuilder objCommandBuilder = new SqlCommandBuilder(daAuthors);//构建sql命令
            daAuthors.Update(dsMaster, "city_users");//更新
            //daAuthors.UpdateCommand = updatecomm;
            //daAuthors.UpdateCommand.ExecuteNonQuery();
            objConn.Close();