XML查询，没有则创建

if (File.Exists(xmlPath + "\\" + xmlName)) //判断文件是否寸在
                {
    //存在的情况下
                    XmlDocument xmldoc = new XmlDocument();
                    xmldoc.Load(xmlPath + "\\" + xmlName);
                    //存在文件
                    XmlNode root = xmldoc.SelectSingleNode("History");
                    XmlElement bak = xmldoc.CreateElement("Bak");
                    root.AppendChild(bak);

                    XmlElement bakTime = xmldoc.CreateElement("BakTime");
                    bakTime.InnerText = DateTime.Now.ToString();
                    bak.AppendChild(bakTime); //备份时间

                    XmlElement bakName = xmldoc.CreateElement("BakName");
                    bakName.InnerText = dbFileName;
                    bak.AppendChild(bakName); // 备份的名字

                    XmlElement DataSource = xmldoc.CreateElement("DataSource");
                    DataSource.InnerText = dataSource;
                    bak.AppendChild(DataSource); //数据源

                    XmlElement Database = xmldoc.CreateElement("Database");
                    Database.InnerText = database;
                    bak.AppendChild(Database); //数据库名称

                    XmlElement DatabaseUser = xmldoc.CreateElement("UserID");
                    DatabaseUser.InnerText = userID;
                    bak.AppendChild(DatabaseUser); //数据库用户名

                    XmlElement Password = xmldoc.CreateElement("Password");
                    Password.InnerText = password;
                    bak.AppendChild(Password); // 数据库密码

                    XmlElement UserName = xmldoc.CreateElement("StaffName");
                    UserName.InnerText = staffName;
                    bak.AppendChild(UserName); //备份人

                    xmldoc.Save(xmlPath + "\\" + xmlName);

                }
                else
                {
                    //不存在文件
                    Directory.CreateDirectory(xmlPath);//创建该文件

                    XmlDocument xmldoc = new XmlDocument();

                    XmlNode xmlnode = xmldoc.CreateXmlDeclaration("1.0", "gb2312", null);
                    xmldoc.AppendChild(xmlnode);

                    XmlElement root = xmldoc.CreateElement("History");
                    xmldoc.AppendChild(root);
                    XmlElement bak = xmldoc.CreateElement("Bak");
                    root.AppendChild(bak);

                    XmlElement bakTime = xmldoc.CreateElement("BakTime");
                    bakTime.InnerText = DateTime.Now.ToString();
                    bak.AppendChild(bakTime); //备份时间

                    XmlElement bakName = xmldoc.CreateElement("BakName");
                    bakName.InnerText = dbFileName;
                    bak.AppendChild(bakName); // 备份的名字

                    XmlElement DataSource = xmldoc.CreateElement("DataSource");
                    DataSource.InnerText = dataSource;
                    bak.AppendChild(DataSource); //数据源

                    XmlElement Database = xmldoc.CreateElement("Database");
                    Database.InnerText = database;
                    bak.AppendChild(Database); //数据库

                    XmlElement DatabaseUser = xmldoc.CreateElement("UserID");
                    DatabaseUser.InnerText = userID;
                    bak.AppendChild(DatabaseUser); //数据库用户名

                    XmlElement Password = xmldoc.CreateElement("Password");
                    Password.InnerText = password;
                    bak.AppendChild(Password); // 数据库密码

                    XmlElement UserName = xmldoc.CreateElement("StaffName");
                    UserName.InnerText = staffName;
                    bak.AppendChild(UserName); //备份人

                    xmldoc.Save(xmlPath + "\\" + xmlName);
                }