Xmldocument as xmlvalue context value question

Question

why is it that when i use an xmldocument (wrapped by an xmlvalue object) as a context value for xmlqueryexpression.execute() and if my query returns nodes (rather than scalars like string(), etc), the resulting xmlresults' xmlvalue objects return empty string for .asString()?
i'm completely new to this approach for using xmldocument as a starting query context. i'm trying this because i figure doing this is better than using doc() because you get to reuse the same xmlqueryexpressions objects across different documents.
so for instance:
          XmlDocument document = xmlContainer.getDocument("catalog2", XmlDocumentConfig.DEFAULT);
          XmlQueryContext ctx = xmlManager.createQueryContext();
          XmlQueryExpression expr = xmlManager.prepare("/catalog/journal/article", ctx);
          XmlResults results = null;
          try {
               results = expr.execute(new XmlValue(document), ctx);
               List<String> articles = new ArrayList<String>();
               try {
                    if (results != null) {
                         if (results.size() > 0) {
                              XmlValue value = results.next();
                              while (value != null) {
                                   articles.add(value.asString());
                                   value = results.next();
               finally {
                    if (results != null) results.delete();
               assertEquals(2, articles.size()); // correct!
               for (String string : articles) {
                    System.out.println(string);
                    assertFalse(StringUtils.isEmpty(string));  // empty strings!
          finally {
               results.delete();
               expr.delete();
               document.delete();
any ideas? thanks.

Answer 1

Hi wvuong,
You can reuse xmlqueryexpression objects across different documents simply by XmlQueryContext::setVariableValue().
Here is an example in C++( sorry, I'm not good at Java ). Please refere the docs if you want more details about using XmlQueryContext::setVariableValue in Java.
// Define XmlQueryExpression using "doc_name" as Variable
XmlQueryContext qc = mgr.createQueryContext();
qc.setVariableValue("doc_name", "");
string query = "for $node in doc($doc_name) return <l1>{$node}</l1>";
XmlQueryExpression expr = mgr.prepare(query, qc);
// Using the XmlQueryExpression
string docName = collection_name + "/" + "THE_DOC_NAME";
qc.setVariableValue("doc_name", docName);
XmlResults res = expr.execute( qc );