/**
 * Take the received string, which is an XML query expression,
 * compile it, and store the compiled query locally.  Note
 * that for now, we only support XPath because that's what
 * Xalan supports.
 *
 * @param queryExpr The XPath expression to compile
 */
public void compileXQExpr(String queryExpr, String opName)
    throws StandardException
{
    try {

        /* The following XPath constructor compiles the expression
         * as part of the construction process.  We pass a null
         * namespace resolver object so that the implementation will
         * provide one for us, which means prefixes will not be resolved
         * in the query (Xalan will just throw an error if a prefix
         * is used).  In the future we may want to revisit this
         * to make it easier for users to query based on namespaces.
         */
        XPathEvaluator eval = (XPathEvaluator)
            dBuilder.getDOMImplementation().getFeature("+XPath", "3.0");
        query = eval.createExpression(queryExpr, null);

        this.queryExpr = queryExpr;
        this.opName = opName;
        this.recompileQuery = false;

    } catch (Throwable te) {

        /* Something went wrong during compilation of the
         * expression; wrap the error and re-throw it.
         * Note: we catch "Throwable" here to catch as many
         * Xalan-produced errors as possible in order to
         * minimize the chance of an uncaught Xalan error
         * (such as a NullPointerException) causing Derby
         * to fail in a more serious way.  In particular, an
         * uncaught Java exception like NPE can result in
         * Derby throwing "ERROR 40XT0: An internal error was
         * identified by RawStore module" for all statements on
         * the connection after the failure--which we clearly
         * don't want.  If we catch the error and wrap it,
         * though, the statement will fail but Derby will
         * continue to run as normal. 
         */
        throw StandardException.newException(
            SQLState.LANG_XML_QUERY_ERROR, te, opName, te.getMessage());

    }
}