How do you specify node result order using XPath?

Question

I have the following XML, which is generated by a 3rd-party library:

<PhoneNumbers>
    <PhoneNumber Key="1">123-456-7890</PhoneNumber>
    <PhoneNumber Key="2">234-567-8901</PhoneNumber>
    <PhoneNumber Key="3">345-678-9012</PhoneNumber>
</PhoneNumbers>

The issue is that I should not depend on the values of the Key attribute (a) appearing in order, or (b) beginning at 1. More so the latter, but I want this processing to be as safe as possible.

What I need to do is get a list of the phone numbers, sorted by the Key value (ascending). So by using XmlNode.SelectNodes I would like the resulting XmlNodeList to contain the PhoneNumber nodes in the proper order, not necessarily in the order they appear.

How can this be accomplished using XPath?
Is this possible to do directly?

If it makes a difference, I'm using .NET 2.0.

Answer 1

The XPathExpression class provides an AddSort method:

http://msdn.microsoft.com/en-us/library/system.xml.xpath.xpathexpression.aspx

Answer 2

Xpath itself does not define anything for that.

For C#.NET, this may be what you're looking for: http://social.msdn.microsoft.com/forums/en-US/xmlandnetfx/thread/ba975e0e-e0c7-4868-9acc-11d589cafc70/

Answer 3

This can't be accomplished with XPath. If you were using an XPathDocument you could use the AddSort method.

However if you are already using XmlDocument (and/or need to be able to update the XML DOM) its probably just a easy to dump the result of SelectNodes into a SortedDictionary using the value of the Key attribute as the Key value.

Answer 4

Here's an example of how to do it with XPathExpression using the AddSort method already mentioned. XPathExpression is available with.Net 2.0 (http://msdn.microsoft.com/en-us/library/system.xml.xpath.xpathexpression.aspx)

private static void XmlTest()
{
    XPathDocument results = new XPathDocument(@"c:\temp\temp.xml");
    XPathNavigator navigator = results.CreateNavigator();
    XPathExpression selectExpression = navigator.Compile("/PhoneNumbers/PhoneNumber");
    XPathExpression sortExpr = navigator.Compile("@Key");
    selectExpression.AddSort(sortExpr, XmlSortOrder.Ascending, XmlCaseOrder.None, "", XmlDataType.Text);
    XPathNodeIterator nodeIterator = navigator.Select(selectExpression);
    int i = 0;
    while (nodeIterator.MoveNext())
    {
        Console.WriteLine(nodeIterator.Current.Value);
        i++;
    }
}