.NET XPath query not coming out right

perropicante · June 15th, 2003, 10:53 AM

Hi,

I've run several XPath queries against an XML document in a program such as XML Spy with great success. When I run the same queries in a small app I wrote that uses the System.Xml.XPath I get mixed results.

I'd like to know what I have to do to get my XPath queries to execute properly.

I want to use this class to extract parts of an XML document sent over the web to create various class instances. If there's a better way of doing this, feel free to suggest it!

Here's the XML doc.

Code:

<PersonProfile>
    <Table>
        <id>1</id>
        <firstname>Michael</firstname>
        <lastname>Gradek</lastname>
        <birthdate>1980-11-13T00:00:00.0000000-05:00</birthdate>
    </Table>
</PersonProfile>

Here's the class that executes the XPath query

Code:

using System;
using System.Xml;
using System.Xml.XPath;

namespace blackbook
{
    /// <summary>
    /// Allows for quick queries on an XML document using XPath.
    /// </summary>
    class XmlQuerier
    {
        private XPathDocument xpathdoc;
        private XPathNavigator xpathnav;

        /// <summary>
        /// Creates an XmlQuerier
        /// </summary>
        /// <param name="xmlurl">the url from which to get the XML document</param>
        public XmlQuerier(string xmlurl)
        {
            xpathdoc = new XPathDocument(xmlurl);
            xpathnav = xpathdoc.CreateNavigator();
        }

        /// <summary>
        /// Creates an XmlQuerier
        /// </summary>
        /// <param name="xmltext">The <seealso cref="System.Xml.XmlTextReader"/>XmlTextReader 
        /// from which to get the XML document</param>
        public XmlQuerier(XmlTextReader xmltext)
        {
            xpathdoc = new XPathDocument(xmltext);
            xpathnav = xpathdoc.CreateNavigator();
        }

        /// <summary>
        /// Gets a variable length array of strings corresponding to the XPath query results
        /// </summary>
        /// <param name="selectexpr">The XPath expression used to query. The XPath must be properly formed.</param>
        /// <returns>A variable length array of strings</returns>
        public string[] XPathQuery(string selectexpr)
        {
            string[] response;
            XPathExpression xpathexpr;
            XPathNodeIterator xpathnode;

            try
            {
                // Create a node interator to select nodes and move through them (read-only)
                this.xpathnav.MoveToRoot();
                xpathexpr = this.xpathnav.Compile(selectexpr);
                xpathnode = xpathnav.Select (xpathexpr);
                response = new string[xpathnode.Count];

                for(int i = 0; i < xpathnode.Count; i++, xpathnode.MoveNext())
                    response[i] = xpathnode.Current.Value;                                }
            catch (System.Xml.XmlException e)
            {
                response = new string[1];
                response[0] = e.ToString();
            }

            return response;
        }
    }
}

Here's the app code that calls the xml query

Code:

using System;
using System.Xml;
using System.Xml.XPath;

namespace xmlquery
{
    /// <summary>
    /// Summary description for Class1.
    /// </summary>
    class QueryTest
    {
        public static string url = @"C:\Documents and Settings\Mike Gradek\Desktop\Test\person.xml";

        [STAThread]
        static void Main(string[] args)
        {
            if(args.Length != 1)
                Console.WriteLine("Usage: xmlquery.exe <xpath query>");
            else
            {
                QueryTest querytest = new QueryTest();
                querytest.Run(QueryTest.url, args[0]);
            }
        }

        public void Run(string url, string query)
        {
            Console.WriteLine("XPath Test started ...");
            blackbook.XmlQuerier xmlquery = new blackbook.XmlQuerier(url);

            Console.WriteLine("Query: " + query);
            foreach(string s in xmlquery.XPathQuery(query))
                Console.WriteLine(s);
        }
    }
}

Here's the XPath query I run in XML Spy
//firstname

which yields the firstname.

When I run the same query in my little app, I get the entire document content returned as a string. Here's the program output

prompt> xmlquery.exe //firstname
XPath Test started ...
Query: //firstname
1MichaelGradek1980-11-13T00:00:00.0000000-05:00

But it should return
XPath Test started ...
Query: //firstname
Michael Gradek

What is it that I'm doing wrong? I'm simply trying to extract the contents of nodes through XPath queries...

Any insight would be greatly appreciated!

Thanks,
Mike