Question

In P.S. of this posting you can find a C# code snippet, which uses XSLT transformation + RegEx matching to get currency rate value from an XML document. Please read my question inline quoted by

//+

…

//-

comment lines group.

Thank you.

P.S. Code:

   string currencyCode = "RUB";
var xml = new StringReader( 
    @"<gesmes:Envelope 
        xmlns:gesmes='http://www.gesmes.org/xml/2002-08-01' 
        xmlns{{EmptyNameSpace}} ='http://www.ecb.int/vocabulary/2002-08-01/eurofxref'>
        <gesmes:subject>Reference rates</gesmes:subject>
        <gesmes:Sender>
        <gesmes:name>European Central Bank</gesmes:name>
    </gesmes:Sender>
    <Cube>
        <Cube time='2012-06-27'>
        <Cube currency='USD' rate='1.2478' />
        <Cube currency='RUB' rate='41.1252' />
        <Cube currency='ZAR' rate='10.4601' />
        </Cube>
    </Cube>
    </gesmes:Envelope>"
            .Replace("{{EmptyNameSpace}}", ":ns1")
            //+
            // I'd like to get this code working the same way as it does now
            // producing
            //
            // Result: EUR/RUB => 41.1252
            //
            // output but when the above code line will be commented
            // and the below code line uncommented
            //-
            //.Replace("{{EmptyNameSpace}}", "") 
);

var xslt = new XmlTextReader(new StringReader(
@"<xsl:stylesheet version='2.0' 
    xmlns:xsl='http://www.w3.org/1999/XSL/Transform'
    xmlns:gesmes='http://www.gesmes.org/xml/2002-08-01' 
    xmlns:ns1 ='http://www.ecb.int/vocabulary/2002-08-01/eurofxref'
    >

<xsl:variable name='x1' select='gesmes:Envelope/Cube/Cube/Cube[@currency=""{0}""]' />
<xsl:template match='gesmes:Envelope'>
  [<xsl:apply-templates select='$x1' />]
</xsl:template>
<xsl:template match='Cube'>
    <xsl:value-of select='@rate' />
</xsl:template>
</xsl:stylesheet>".Replace("{0}", currencyCode)  

));

var xDoc = new XPathDocument(xml);
var xTr = new System.Xml.Xsl.XslCompiledTransform(); 
xTr.Load(xslt) ;

StringBuilder sb = new StringBuilder(); 
StringWriter writer = new StringWriter(sb); 
xTr.Transform(xDoc, null, writer);

string pattern = @"\[(?'name'[0-9]*\.[0-9]*)\]";

System.Console.WriteLine(
    "Result: EUR/{0} => {1}",
    currencyCode, 
    Regex.Match(sb.ToString(), pattern)
   .Groups["name"].Value);    

// Result: EUR/RUB => 41.1252

Answer 1

As far as I can tell from looking at that code, your problems is handling the default namespace in XPath:

• As long as {{EmptyNameSpace}} is :ns1, everything’s fine – in your Xml document, the namespaces http://www.gesmes.org/xml/2002-08-01 and http://www.ecb.int/vocabulary/2002-08-01/eurofxref with the prefixes gesmes and ns1 are defined; your Xml document uses identifiers such as <gesmes:Envelope> from gesmes and others, namely <Cube>, that are not associated with any namespace. In the XSLT code, you are using XPath expressions, such as (here shortened) gesmes:Envelope/Cube/Cube/Cube, which is fine, as this expression refers to an <Envelope> element from the namespace declared with the gesmes prefix, as well as to <Cube> elements without a namespace.
• Once you set {{EmptyNameSpace}} to an empty string, this changes: Now, http://www.ecb.int/vocabulary/2002-08-01/eurofxref is the default namespace of your document. Hence, the <Cube> elements in your document are considered to belong to that namespace. Your XPath expression, however, still considers the <Cube> elements that appear in the XPath as having no namespace – they do not have any namespace prefix and XPath doesn’t know about default namespaces.

As a solution, you should add namespace prefixes to your XPath expression – if the <Cube> elements belong to the http://www.ecb.int/vocabulary/2002-08-01/eurofxref namespace, your XPath should read like this:

gesmes:Envelope/ns1:Cube/ns1:Cube/ns1:Cube

(Of course, the other XPath expressions in your XSLT have to be adapted accordingly.)

Please let me know if you need any further explanations on this – or whether I’ve gotten on the wrong track with my assumptions.

Update: Here’s what the XSLT should look like in order to work if the Xml document has the default namespace:

<xsl:stylesheet version="2.0" xmlns:xsl='http://www.w3.org/1999/XSL/Transform' xmlns:gesmes='http://www.gesmes.org/xml/2002-08-01' xmlns:ns1='http://www.ecb.int/vocabulary/2002-08-01/eurofxref'>

    <xsl:variable name='x1' select='gesmes:Envelope/ns1:Cube/ns1:Cube/ns1:Cube[@currency="RUB"]'/>

    <xsl:template match='gesmes:Envelope'>
        [<xsl:apply-templates select='$x1'/>]
    </xsl:template>

    <xsl:template match='ns1:Cube'>
        <xsl:value-of select='@rate'/>
    </xsl:template>

</xsl:stylesheet>