C# 动态修改Web.config

        protected void btnSet_Click(object sender, EventArgs e)
        {
            XmlDocument xmlDoc=new XmlDocument();
            string filename = Server.MapPath("/")+"Web.config";
            xmlDoc.Load(filename);
            XmlNode root = xmlDoc.SelectSingleNode("configuration");
            XmlNode conNode = root.SelectSingleNode("connectionStrings");
            XmlNodeList conNodeList = conNode.ChildNodes;
            bool haveconnectionString = false;
            string constring="data source=" + tbServer.Text.Trim() + ";user="+tbUser.Text.Trim()+";pwd="+tbPwd.Text.Trim()+";Initial Catalog="+tbDB.Text+";";
            foreach (XmlNode node in conNodeList)
            {
                XmlElement element = (XmlElement)node;  //将子节点类型转换为XmlElecment类型
                if (element.GetAttribute("providerName") == "System.Data.SqlClient")
                {
                    element.SetAttribute("connectionString", constring);
                    element.SetAttribute("name", "connectionString1");
                    haveconnectionString = true;
                }
            }
            if (haveconnectionString == false)
            {
                XmlElement xel= xmlDoc.CreateElement("add");
                xel.SetAttribute("name", "connectionString1");
                xel.SetAttribute("connectionString", constring);
                xel.SetAttribute("providerName", "System.Data.SqlClient");
                conNode.AppendChild(xel);
            }
            xmlDoc.Save(filename);
        }