Create XML Nodes based on XPath?

Question

Does anyone know of an existing means of creating an XML hierarchy programatically from an XPath expression?

For example if I have an XML fragment such as:

Given the XPath expression /feed/entry/content/@source I would have:

I realize this is possible using XSLT but due to the dynamic nature of what I'm trying to accomplish a fixed transformation won't work.

I am working in C# but if someone has a solution using some other language please chime in.

Thanks for the help!

xcud_61396 · Answer

In the example you present the only thing being created is the attribute ...

XmlElement element = (XmlElement)doc.SelectSingleNode("/feed/entry/content");
if (element != null)
    element.SetAttribute("source", "");

If what you really want is to be able to create the hierarchy where it doesn't exist then you could your own simple xpath parser. I don't know about keeping the attribute in the xpath though. I'd rather cast the node as an element and tack on a .SetAttribute as I've done here:


static private XmlNode makeXPath(XmlDocument doc, string xpath)
{
    return makeXPath(doc, doc as XmlNode, xpath);
}

static private XmlNode makeXPath(XmlDocument doc, XmlNode parent, string xpath)
{
    // grab the next node name in the xpath; or return parent if empty
    string[] partsOfXPath = xpath.Trim('/').Split('/');
    string nextNodeInXPath = partsOfXPath.First();
    if (string.IsNullOrEmpty(nextNodeInXPath))
        return parent;

    // get or create the node from the name
    XmlNode node = parent.SelectSingleNode(nextNodeInXPath);
    if (node == null)
        node = parent.AppendChild(doc.CreateElement(nextNodeInXPath));

    // rejoin the remainder of the array as an xpath expression and recurse
    string rest = String.Join("/", partsOfXPath.Skip(1).ToArray());
    return makeXPath(doc, node, rest);
}

static void Main(string[] args)
{
    XmlDocument doc = new XmlDocument();
    doc.LoadXml("");

    makeXPath(doc, "/feed/entry/data");
    XmlElement contentElement = (XmlElement)makeXPath(doc, "/feed/entry/content");
    contentElement.SetAttribute("source", "");

    Console.WriteLine(doc.OuterXml);
}

user_279098 · Answer

If the XPath string is processed from back to front, its easier to process non rooted XPaths eg. //a/b/c... It should support Gordon's XPath syntax too although I have not tried...

static private XmlNode makeXPath(XmlDocument doc, string xpath)
{
    string[] partsOfXPath = xpath.Split('/');
    XmlNode node = null;
    for (int xpathPos = partsOfXPath.Length; xpathPos > 0; xpathPos--)
    {
        string subXpath = string.Join("/", partsOfXPath, 0, xpathPos);
        node = doc.SelectSingleNode(subXpath);
        if (node != null)
        {
            // append new descendants
            for (int newXpathPos = xpathPos; newXpathPos < partsOfXPath.Length; newXpathPos++)
            {
                node = node.AppendChild(doc.CreateElement(partsOfXPath[newXpathPos]));
            }
            break;
        }
    }

    return node;
}

Create XML Nodes based on XPath?

12 Answers