如何把数据库里的数据用XML的形式读出来

string sql = "SELECT id,name FROM content FOR XML AUTO,XMLDATA";
SqlConnection conn =new SqlConnection("server=.;uid=sa;database=TextProject" );
SqlCommand cmd=new SqlCommand(sql,conn);
conn.Open();
XmlTextReader objXmlReader = (XmlTextReader)cmd.ExecuteXmlReader();
DataSet ds = new DataSet();
ds.DataSetName = "XML";
ds.ReadXml(objXmlReader,XmlReadMode.Fragment);
ds.WriteXml(Server.MapPath("XML.xml"));
conn.Close();