Question

I am tryng to sort a result from an xpath query but it fails.

Ooutput:

ABC
DEF

But I am expecting:

DEF
ABC

The source code looks like this, it uses an XML expression and sorts the result:

var doc = new XPathDocument("testmsg2.xml");
var nav = doc.CreateNavigator();

const string query = "//Z/X/Code";

var expr = nav.Compile(query);
expr.AddSort("Code",
             XmlSortOrder.Descending,
             XmlCaseOrder.None,
             "",
             XmlDataType.Text);

switch (expr.ReturnType)
{                
    case XPathResultType.NodeSet:
        var nodes = (XPathNodeIterator)nav.Evaluate(expr);

        while (nodes != null && nodes.MoveNext())
        {
            if (nodes.Current == null)
                continue;

            if (nodes.Current.HasChildren)
            {
                var childIter = nodes.Current.SelectChildren(XPathNodeType.All);

                while (childIter.MoveNext())
                {
                    if (childIter.Current != null)
                        Console.WriteLine(childIter.Current.Value);
                }
            }
            else
            {
                Console.WriteLine(nodes.Current.Value);
            }
        }

        break;
}

The XML file is simplified for this example:

<?xml version="1.0" encoding="utf-8"?>
<Z>
  <X>
    <Code>ABC</Code>
  </X>
  <X>
    <Code>DEF</Code>
  </X>
</Z>

Answer 1

The AddSort method takes an XPath expression that is contextually bound to the XPathExpression you’ve compiled. In your case, the XPathExpression is compiled against the <Code> element. Doing AddSort("Code") implies that you have the following XML:

<Code>
    <Code>
    </Code>
</Code>

Instead, you can either compile your expression to X:

const string query = "//Z/X";

Or you can sort on the current node (being Code), .:

expr.AddSort(".", XmlSortOrder.Descending, XmlCaseOrder.None, "", XmlDataType.Text);