Saxonica - .NET API - XQuery - XPDY0002: The context item for axis step root/descendant::xxx is absent - saxon

Question

I'm getting same error as this question, but with XQuery:
SaxonApiException: The context item for axis step ./CLIENT is absent
When running from the command line, all is good. So I don't think there is a syntax problem with the XQuery itself. I won't post the input file unless needed.
The XQuery is displayed with a Console.WriteLine before the error appears:
----- Start: XQUERY:
(: FLWOR = For Let Where Order-by Return :)
<MyFlightLegs>
{
for $flightLeg in //FlightLeg
where $flightLeg/DepartureAirport = 'OKC' or $flightLeg/ArrivalAirport = 'OKC'
order by $flightLeg/ArrivalDate[1] descending
return $flightLeg
}
</MyFlightLegs>
----- End : XQUERY:
Error evaluating (<MyFlightLegs {for $flightLeg in root/descendant::FlightLeg[DepartureAirport = "OKC" or ArrivalAirport = "OKC"] ... return $flightLeg}/>) on line 4 column 20
XPDY0002: The context item for axis step root/descendant::FlightLeg is absent
I think that like the other question, maybe my input XML file is not properly specified.
I took the samples/cs/ExamplesHE.cs run method of the XQuerytoStream class.
Code there for easy reference is:
public class XQueryToStream : Example
{
public override string testName
{
get { return "XQueryToStream"; }
}
public override void run(Uri samplesDir)
{
Processor processor = new Processor();
XQueryCompiler compiler = processor.NewXQueryCompiler();
compiler.BaseUri = samplesDir.ToString();
compiler.DeclareNamespace("saxon", "http://saxon.sf.net/");
XQueryExecutable exp = compiler.Compile("<saxon:example>{static-base-uri()}</saxon:example>");
XQueryEvaluator eval = exp.Load();
Serializer qout = processor.NewSerializer();
qout.SetOutputProperty(Serializer.METHOD, "xml");
qout.SetOutputProperty(Serializer.INDENT, "yes");
qout.SetOutputStream(new FileStream("testoutput.xml", FileMode.Create, FileAccess.Write));
Console.WriteLine("Output written to testoutput.xml");
eval.Run(qout);
}
}
I changed to pass the Xquery file name, the xml file name, and the output file name, and tried to make a static method out of it. (Had success doing the same with the XSLT processor.)
static void DemoXQuery(string xmlInputFilename, string xqueryInputFilename, string outFilename)
{
// Create a Processor instance.
Processor processor = new Processor();
// Load the source document
DocumentBuilder loader = processor.NewDocumentBuilder();
loader.BaseUri = new Uri(xmlInputFilename);
XdmNode indoc = loader.Build(loader.BaseUri);
XQueryCompiler compiler = processor.NewXQueryCompiler();
//BaseUri is inconsistent with Transform= Processor?
//compiler.BaseUri = new Uri(xqueryInputFilename);
//compiler.DeclareNamespace("saxon", "http://saxon.sf.net/");
string xqueryFileContents = File.ReadAllText(xqueryInputFilename);
Console.WriteLine("----- Start: XQUERY:");
Console.WriteLine(xqueryFileContents);
Console.WriteLine("----- End : XQUERY:");
XQueryExecutable exp = compiler.Compile(xqueryFileContents);
XQueryEvaluator eval = exp.Load();
Serializer qout = processor.NewSerializer();
qout.SetOutputProperty(Serializer.METHOD, "xml");
qout.SetOutputProperty(Serializer.INDENT, "yes");
qout.SetOutputStream(new FileStream(outFilename,
FileMode.Create, FileAccess.Write));
eval.Run(qout);
}
Also two questions regarding "BaseURI".
1. Should it be a directory name, or can it be same as the Xquery file name?
2. I get this compile error: "Cannot implicity convert to "System.Uri" to "String".
compiler.BaseUri = new Uri(xqueryInputFilename);
It's exactly the same thing I did for XSLT which worked. But it looks like BaseUri is a string for XQuery, but a real Uri object for XSLT? Any reason for the difference?

Answer 1

You seem to be asking a whole series of separate questions, which are hard to disentangle.
Your C# code appears to be compiling the query
<saxon:example>{static-base-uri()}</saxon:example>
which bears no relationship to the XQuery code you supplied that involves MyFlightLegs.
The MyFlightLegs query uses //FlightLeg and is clearly designed to run against a source document containing a FlightLeg element, but your C# code makes no attempt to supply such a document. You need to add an eval.ContextItem = value statement.
Your second C# fragment creates an input document in the line
XdmNode indoc = loader.Build(loader.BaseUri);
but it doesn't supply it to the query evaluator.
A base URI can be either a directory or a file; resolving relative.xml against file:///my/dir/ gives exactly the same result as resolving it against file:///my/dir/query.xq. By convention, though, the static base URI of the query is the URI of the resource (eg file) containing the source query text.
Yes, there's a lot of inconsistency in the use of strings versus URI objects in the API design. (There's also inconsistency about the spelling of BaseURI versus BaseUri.) Sorry about that; you're just going to have to live with it.

Answer 2

Bottom line solution based on Michael Kay's response; I added this line of code after doing the exp.Load():
eval.ContextItem = indoc;
The indoc object created earlier is what relates to the XML input file to be processed by the XQuery.