how to use XPath with XDocument?

There is a similar question, but it seems that the solution didn't work out in my case: https://stackoverflow.com/questions/3715936/weirdness-with-xdocument-xpath-and-namespaces

Here is the XML I am working with:

<?xml version="1.0" encoding="utf-8"?>
<Report Id="ID1" Type="Demo Report" Created="2011-01-01T01:01:01+11:00" Culture="en" xmlns="http://demo.com/2011/demo-schema">
    <ReportInfo>
        <Name>Demo Report</Name>
        <CreatedBy>Unit Test</CreatedBy>
    </ReportInfo>
</Report>

And below is the code that I thought it should be working but it didn't...

XDocument xdoc = XDocument.Load(@"C:\SampleXML.xml");
XmlNamespaceManager xnm = new XmlNamespaceManager(new NameTable()); 
xnm.AddNamespace(String.Empty, "http://demo.com/2011/demo-schema");
Console.WriteLine(xdoc.XPathSelectElement("/Report/ReportInfo/Name", xnm) == null);

Does anyone have any ideas? Thanks.

If you have XDocument it is easier to use LINQ-to-XML:

var document = XDocument.Load(fileName);
var name = document.Descendants(XName.Get("Name", @"http://demo.com/2011/demo-schema")).First().Value;

If you are sure that XPath is the only solution you need:

using System.Xml.XPath;

var document = XDocument.Load(fileName);
var namespaceManager = new XmlNamespaceManager(new NameTable());
namespaceManager.AddNamespace("empty", "http://demo.com/2011/demo-schema");
var name = document.XPathSelectElement("/empty:Report/empty:ReportInfo/empty:Name", namespaceManager).Value;

XPath 1.0, which is what MS implements, does not have the idea of a default namespace. So try this:

XDocument xdoc = XDocument.Load(@"C:\SampleXML.xml");
XmlNamespaceManager xnm = new XmlNamespaceManager(new NameTable()); 
xnm.AddNamespace("x", "http://demo.com/2011/demo-schema");
Console.WriteLine(xdoc.XPathSelectElement("/x:Report/x:ReportInfo/x:Name", xnm) == null);

you can use the example from Microsoft - for you without namespace:

using System.Xml.Linq;
using System.Xml.XPath;
var e = xdoc.XPathSelectElement("./Report/ReportInfo/Name");     

should do it

To work w/o default namespace suffix, I automatically expand the path.

Usage: SelectElement(xdoc.Root, "/Report/ReportInfo/Name");

private static XElement SelectElement(XElement startElement, string xpathExpression, XmlNamespaceManager namespaceManager = null) {
    // XPath 1.0 does not have support for default namespace, so we have to expand our path.
    if (namespaceManager == null) {
        var reader = startElement.CreateReader();
        namespaceManager = new XmlNamespaceManager(reader.NameTable);
    }
    var defaultNamespace = startElement.GetDefaultNamespace();
    var defaultPrefix = namespaceManager.LookupPrefix(defaultNamespace.NamespaceName);
    if (string.IsNullOrEmpty(defaultPrefix)) {
        defaultPrefix = "ᆞ";
        namespaceManager.AddNamespace(defaultPrefix, defaultNamespace.NamespaceName);
    }
    xpathExpression = AddPrefix(xpathExpression, defaultPrefix);
    var selected = startElement.XPathSelectElement(xpathExpression, namespaceManager);
    return selected;
}

private static string AddPrefix(string xpathExpression, string prefix) {
    // Implementation notes:
    // * not perfect, but it works for our use case.
    // * supports: "Name~~" "~~/Name~~" "~~@Name~~" "~~[Name~~" "~~[@Name~~"
    // * does not work in complex expressions like //*[local-name()="HelloWorldResult" and namespace-uri()='http://tempuri.org/']/text()
    // * does not exclude strings like 'string' or function like func()
    var s = Regex.Replace(xpathExpression, @"(?<a>/|\[@|@|\[|^)(?<name>\w(\w|[-])*)", "${a}${prefix}:${name}".Replace("${prefix}", prefix));
    return s;
}

If anyone has a better solution to find element and attribute names, feel free to change this post.