在这种情况下我如何使用LINQ2XML？

XDocument doc = XDocument.Load("example.xml");

var query = from item in doc.Descendants("item")
            where item.Attribute("id").Value == "123"
            select item;

XElement newItem = new XElement("item",
    new XAttribute("id", "456"),
    new XElement("name", "New Item"),
    new XElement("price", "99.99")
);

var itemToUpdate = doc.Descendants("item").Where(i => i.Attribute("id").Value == "123").FirstOrDefault();
if (itemToUpdate != null)
{
    itemToUpdate.Element("name").Value = "Updated Item";
}

var itemToDelete = doc.Descendants("item").Where(i => i.Attribute("id").Value == "123").FirstOrDefault();
if (itemToDelete != null)
{
    itemToDelete.Remove();
}

doc.Save("example.xml");