linq to xml查询XML元素并计算指定的值

         private void QueryElementByCompute()
         {   ///导入XML文件
                   string xmlFilePath = Server.MapPath("Data/Books.xml");
                   XElement xes = XElement.Load(xmlFilePath);
                   ///查询根元素
                   IEnumerable<XElement> elements = from e in xes.Elements("Book")
                                                                                              where e.Attribute("ID").Value.IndexOf("10") > -1
                                                                                              orderby (string)e.Element("Name") descending
                                                                                              select e;
                   ///计算价格的平均值
                   decimal avg = elements.Average(e => decimal.Parse(e.Element("Price").Value));
                   Response.Write("Average:" + avg.ToString() + "<br />");
         }