XslTransform class, now obsoleted in .NET 2.0 has a very nice feature - it allows to perform pull-mode XSL transformations. The result of the transformation can be an XmlReader object and the actual transformation occurs only when you call that reader methods. That feature, traditionally overlooked and rarely mentioned (come on, who cares about perf nowadays, right?) enables very efficient XML pipelining with no temporary XML stores. If a component (such as SqlXml class) accepts XML as an instance of XmlReader and you need to feed it with XSLT output that is easy and efficient. I was trying to promote this feature with XmlTransformingReader class, which you can find in the Mvp.Xml library.
Now, new and shiny XslCompiledTransform class doesn't support this feature anymore, transformation output is now only Stream, TextWriter or XmlWriter, so it's pure push-mode transformer. That actually simplified API a bit, but now in a scenario when you need a transformation result as an XmlReader one needs 1) a temporary XML storage and 2) write nasty complicated code like this:
// Load XSL transformation
XslCompiledTransform xform = new XslCompiledTransform();
xform.Load (xslPath);
// Execute/Cache results
XmlDocument resultsDoc = new XmlDocument();
XPathNavigator resultsNav = resultsDoc.CreateNavigator();
// using makes sure that we flush the writer at the end
using (XmlWriter writer = resultsNav.AppendChild())
{
xform.Transform(XmlData.CreateReader(), writer);
}
// Return results
SqlXml retSqlXml = new SqlXml (resultsNav.ReadSubtree());
return (retSqlXml);
It's from Michael Rys's excellent webcast on "Managing XML Data on the Database with SQL Server 2005 and Visual Studio 2005".
Temporary XML document, what can be worse? In .NET 1.X this could be done much easier and efficient:
// Load XSL transformation XslTransform xform = new XslTransform(); xform.Load (xslPath); //Load source XML XPathDocument doc = new XPathDocument(XmlData.CreateReader()); // Return results SqlXml retSqlXml = new SqlXml ( xform.Transform(doc, null, new XmlUrlResolver())); return (retSqlXml);
Now that's a pity .NET 2.0 doesn't add any new XSLT-related functionality, but even cuts off some :( I wonder if this was cut because it was unfeasible to implement with new XslCompiledTransform architecture or the reason was a different one. Oh well, I filed this issue as a bug. Go vote for it if you care.
One interesting point Norm raised is how come this glitch happened:
I think what pains me most about this situation is that XInclude was in development for just over five years. It went through eleven drafts[1] including three Candidate Recommendations.Basically I disagree. Of course this incompatibility wasn't unnoticed. Moreover you can find the following in the "DocBook Technical Committee Meeting Minutes: 19 Nov 2002":
Why didn't we notice this until several months after XInclude was a Recommendation?
615587 Support xml:baseYou get the idea of what is the common solution - just declare xml:base and xml:lang in your schema.
Any object to adding xml:base to the common attributes? None.
Accepted.
And what about better solutions? Norm talks about fixing either XML Schema or XInclude. I don't see why XInclude needs to be fixed here. It's clear that if a fragment comes from a different place its base URI must be preserved somehow, otherwise say good bye to relative URIs in included fragment. And xml:base is currently the only feasible facility of base URI manipulation. But when it comes to XML Schema I see plenty of room for improvements - it could either allow to define globally allowed attributes or to allow xml: attributes to appear anywhere, just like xsi:type at al.
What's wrong with the latter solution? xml:base, xml:lang, xml:space, xml:id - isn't it ridiculous to be forced to declare them on every element in XML Schema? They are orthogonal to validation and so XML Schema validation should be orthogonal to them.
Another interesting tidbit - this issue was reported to the MSDN Product Feedback Center by kzu and his suggestion to introduce a flag to the XmlSchemaValidationFlags enum saying that xml: attributes should be ignored during validation seems to be favorable by Microsoft. There is a chance that in .NET 2.0 XML Schema processor will optionally allow xml:base and friends even if not declared in schema. If you like it - go vote for this suggestion. I did.