用XElement附加XML

Question

PurchaseList.xml

<purchaseList>
    <user id="13004">
      <books>
        <book isbn="1111707154" title="Music Potter 2" author="customer" price="10" currency="RM" />
      </books>
    </user>
</purchaseList>

WebService.cs

xDoc = XDocument.Load(serverPath + "PurchaseList.xml");
XElement xNewBook = (XElement)(from user in xDoc.Descendants("user")
                               where (String)user.Attribute("id") == userID
                               from books in user.Elements("books")
                               select user).Single();

XElement xPurchaseBook = new XElement("book",
    new XAttribute("isbn", xISBN),
    new XAttribute("title", xTitle),
    new XAttribute("author", "customer"),
    new XAttribute("price", xPrice),
    new XAttribute("currency", xCurrency));
xNewBook.Add(xPurchaseBook);
xNewBook.Save(localPath + "PurchaseList.xml");

Output :

<user id="13004">
    <books>
        <book isbn="1111707154" title="Music Potter 2" author="customer" price="10" currency="RM" />
    </books>
    <book isbn="1439056501" title="Harry Potter" author="customer" price="10" currency="RM" />
</user>

Expected output :

<purchaseList>
    <user id="13004">
      <books>
        <!-- Should append inside here -->
        <book isbn="1111707154" title="Music Potter 2" author="customer" price="10" currency="RM" />
        <book isbn="1439056501" title="Harry Potter" author="customer" price="10" currency="RM" />
      </books>
    </user>
</purchaseList>

As you can see, i wish to append the xml file using XElement, but output is ain't i expected, it even delete the tag and append at the wrong position.

Answer 1

Replace xNewBook.Add(xPurchaseBook);

with xNewBook.Element("books").Add(xPurchaseBook);

You are selecting user in LINQ query and adding a new item in that. You need to get books element from the user and should add in that.

OR

You should get the books element and save the entire xDoc instead of xNewBook .

XElement xNewBook = (from user in xDoc.Descendants("user")
                      where (String)user.Attribute("id") == "13004"
                       select user.Element("books")).Single();

and save xDoc -

xDoc.Save(localPath + "PurchaseList.xml");