XPath Version Search

Question

How would I find the node(s) with the max version from the following document:

<GateKeeperFiles>
  <File>
    <Name>GateKeeper.exe</Name>
    <Major>2</Major>
    <Minor>1</Minor>
    <Build>1</Build>
    <Revision>6</Revision>
  </File>
  <File>
    <Name>GateKeeper.exe</Name>
    <Major>1</Major>
    <Minor>1</Minor>
    <Build>1</Build>
    <Revision>9</Revision>
  </File>
</GateKeeperFiles>

Ideally this would be acheived with a single XPath function. I currently have two functions which get me the max major value but I can't seem to progress from there.

/GateKeeperFiles/File[not (Major <= preceding-sibling::File/Major) and not(Major <= following-sibling::File/Major)]

or

/GateKeeperFiles/File[not(/GateKeeperFiles/File/Major > Major)]

Cheers, Steve

Answer 1

If you are using C#, must it be xpath? For example (edited to support multiple files with the same version - post mentioned plural):

        XDocument doc = XDocument.Parse(xml);
        var nodes =
            from file in doc.Document
                .Element("GateKeeperFiles")
                .Elements("File")
            select new {
                   Node = file,
                   Version = new Version(
                     (int) file.Element("Major"),
                     (int) file.Element("Minor"),
                     (int) file.Element("Build"),
                     (int) file.Element("Revision"))
                   } into tmp
                orderby tmp.Version descending
                select tmp;

        var mostRecentVersion = nodes.Select(x => x.Version).FirstOrDefault();
        var files = nodes.TakeWhile(x => x.Version == mostRecentVersion);

        foreach(var file in files) {
            Console.WriteLine("{0}: {1}",
                file.Version,
                (string)file.Node.Element("Name"));
        }

---

Or with 2.0 (from OP comment):

    static int GetVersion(XmlNode element, string xpath) {
        return int.Parse(element.SelectSingleNode(xpath).InnerText);
    }
    static void Main() {
        XmlDocument doc = new XmlDocument();
        doc.LoadXml(xml);

        Version bestVersion = null;
        List<XmlElement> files = new List<XmlElement>();
        foreach (XmlElement file in doc.SelectNodes(
                 "/GateKeeperFiles/File")) {
            Version version = new Version(
                GetVersion(file, "Major"), GetVersion(file, "Minor"),
                GetVersion(file, "Build"), GetVersion(file, "Revision"));
            if (bestVersion == null || version > bestVersion) {
                bestVersion = version;
                files.Clear();
                files.Add(file);
            } else if (version == bestVersion) {
                files.Add(file);
            }
        }
        Console.WriteLine("Version: " + bestVersion);
        foreach (XmlElement file in files) {
            Console.WriteLine(file.SelectSingleNode("Name").InnerText);
        }
    }

Answer 2

I have used xsl:sort to achieve similar stuff. Don't remember the exact syntax but try this

After this select the first or the last element. I forgot what is the default behaviour of sort ascending or descending but you can override that with xsl:sort.

Answer 3

The code should be able to run on .Net 2.0 so the LINQ solution although correct will not suit the scinario.

I'm processing the XML in code and not performing a transform so XSLT would not be suitable either.

Cheers

Answer 4

Hi Marc,

I have a similar solution to your .Net 2.0 one, I was just hoping for a nice clean XPath version. Looks like this is another area (like bitwise operators) that XPath just doesn't have the answers for.

Cheers