PL/SQL XMLTYPE ORA-30625

Question

I'm working with a web service that returns the output below. I'm having a hard time building the XMLTYPE variable from the output. I get the following error when trying to output the CreateUserSessionFromInstanceResult

ORA-30625: method dispatch on NULL SELF argument is disallowed

procedure xmltest is

str_xml varchar2(32000);
v_xml XMLTYPE;

BEGIN
str_xml :='<?xml version="1.0" encoding="utf-8"?>
       <soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/"     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
            <soap:Body>
                <CreateUserSessionFromInstanceResponse xmlns="http://archer-tech.com/webservices/">
                    <CreateUserSessionFromInstanceResult>4FFABEE05C4910A31FEC75D5FEDCDFB5</CreateUserSessionFromInstanceResult>
                </CreateUserSessionFromInstanceResponse>
            </soap:Body>
       </soap:Envelope>';
v_xml := XMLTYPE(str_xml);
HTP.P(v_xml.extract('//CreateUserSessionFromInstanceResult/text()').getstringval());

END;

Answer 1

The error is on this line

HTP.P(v_xml.extract('//CreateUserSessionFromInstanceResult/text()').getstringval());

You're getting an error because your XPath expression

//CreateUserSessionFromInstanceResult/text()

matches nothing, and so extract(...) returns NULL. Of course, you can't call getstringval() on NULL, hence the error you see.

The reason your XPath isn't matching is because of namespaces. The xmlns attribute on the <CreateUserSessionFromInstanceResponse> element sets the namespace of this element and of the <CreateUserSessionFromInstanceResult> element it contains to be "http://archer-tech.com/webservices/". On the other hand, your XPath expression is searching for the element with the name CreateUserSessionFromInstanceResult in the default namespace, "".

The fix is to add a third parameter to extract that declares this namespace. You do this in the same way as it appears in the XML:

HTP.P(v_xml.extract('//CreateUserSessionFromInstanceResult/text()',
                    'xmlns="http://archer-tech.com/webservices/"').getstringval());