XML Parsing with Default Namespaces via PL/SQL

In my previous post I covered parsing of XML where a namespace prefix existed for each namespace. What happens when you have to parse XML where some of the XML is in a default namespace? Make up a namespace prefix. No W3C complaint parser will care about what the prefix is in the XML and the prefix in the XPath is as long as the URI (the stuff within the " quotes) is the same for the node in question. Here is a simple example based off the ongoing example

DECLARE
  l_doc       VARCHAR2(2000);
  l_domdoc    dbms_xmldom.DOMDocument;
  l_nodelist  dbms_xmldom.DOMNodeList;
  l_node      dbms_xmldom.DOMNode;
  l_value     VARCHAR2(30);
  l_a_ns      VARCHAR2(30);
  l_both_ns   VARCHAR2(60);

  l_xmltype   XMLTYPE;
  l_empx      XMLTYPE;
  l_index     PLS_INTEGER;
  l_col_ind   PLS_INTEGER;
BEGIN
  l_doc := '<employees xmlns="abc.com/123" xmlns:b="xyz.net/456">
 <emp>
  <name>Scott</name>
  <b:favorites>
   <b:color>red</b:color>
   <b:color>orange</b:color>
  </b:favorites>
 </emp>
 <emp>
  <name>John</name>
  <b:favorites>
   <b:color>blue</b:color>
   <b:color>green</b:color>
  </b:favorites>
 </emp>
</employees>';

  l_a_ns := 'xmlns:a="abc.com/123"';  -- assign random prefix to namespace
  -- assigning a different prefix to this namespace
  l_both_ns := l_a_ns || ' xmlns:c="xyz.net/456"'; -- separated by a space

  l_xmltype := XMLTYPE(l_doc);

  -- Method 4
  dbms_output.new_line;
  dbms_output.put_line('Method 4');
  l_value := l_xmltype.extract('/employees/emp[2]/name/text()', 'xmlns="abc.com/123"').getStringVal();
  dbms_output.put_line('Emp Name: '||l_value);

  -- Method 5
  dbms_output.new_line;
  dbms_output.put_line('Method 5');
  l_index := 1;
  WHILE l_xmltype.Existsnode('/a:employees/a:emp[' || To_Char(l_index) || ']', l_a_ns) > 0
  LOOP
   l_empx := l_xmltype.extract('/a:employees/a:emp[' || To_Char(l_index) || ']', l_a_ns);
   l_col_ind := 1;
   WHILE l_empx.Existsnode('/a:emp/c:favorites/c:color[' || To_Char(l_col_ind) || ']', l_both_ns) > 0
   LOOP
      l_value := l_empx.extract('/a:emp/c:favorites/c:color[' || To_Char(l_col_ind) || ']/text()', l_both_ns).getStringVal();
      dbms_output.put_line('Color: '||l_value);
      l_col_ind := l_col_ind + 1;
   END LOOP;
   l_index := l_index + 1;
  END LOOP;
END;

In the XML, we have a default namespace of "abc.com/123" for the elements and the previous "xyz.net/456" namespace. In the code, I randomly picked a prefix of "a" for the default namespace and so anytime an element in the default namespace is referenced, the corresponding prefix is used.

As Method 4 shows, you could just provide the default namespace as is for the third parm and then there is no need to include a prefix in the XPath itself. I prefer to go the route of method 5 as I have encountered XML where the "default" namespace has changed several nodes deep in the XML. Since the default changes, you need to specify a namespace prefix to keep things in order with the namespace each node resides in.

XML Parsing with Namespaces via PL/SQL

My previous post covered the basics for parsing simple XML in PL/SQL, but most XML has one or more namespaces associated with it. So how do you deal with that? Simple pretty much. Oracle provides a third parm (usually it is the third) to pass namespace URI information along to the underlying parser. I've taken the previous XML and added two namespaces to it and updated the appropriate calls to make this example.

DECLARE
l_doc       VARCHAR2(2000);
l_domdoc    dbms_xmldom.DOMDocument;
l_nodelist  dbms_xmldom.DOMNodeList;
l_node      dbms_xmldom.DOMNode;
l_value     VARCHAR2(30);
l_a_ns      VARCHAR2(30);
l_both_ns   VARCHAR2(60);

l_xmltype   XMLTYPE;
l_empx      XMLTYPE;
l_index     PLS_INTEGER;
l_col_ind   PLS_INTEGER;
BEGIN
l_doc := '<a:employees xmlns:a="abc.com/123" xmlns:b="xyz.net/456">
 <a:emp>
  <a:name>Scott</a:name>
  <b:favorites>
   <b:color>red</b:color>
   <b:color>orange</b:color>
  </b:favorites>
 </a:emp>
 <a:emp>
  <a:name>John</a:name>
  <b:favorites>
   <b:color>blue</b:color>
   <b:color>green</b:color>
  </b:favorites>
 </a:emp>
</a:employees>';

l_domdoc   := dbms_xmldom.newDomDocument(l_doc);
l_a_ns := 'xmlns:a="abc.com/123"';
l_both_ns := l_a_ns || ' xmlns:b="xyz.net/456"'; -- separated by a space

-- Method 1
dbms_output.put_line('Method 1');
-- third parm for namespace info
l_nodelist := dbms_xslprocessor.selectNodes(dbms_xmldom.makeNode(l_domdoc),'/a:employees/a:emp/a:name', l_a_ns);
FOR cur_emp IN 0 .. dbms_xmldom.getLength(l_nodelist) - 1 LOOP
 l_node := dbms_xmldom.item(l_nodelist, cur_emp);
 l_value := dbms_xmldom.getnodevalue(dbms_xmldom.getfirstchild(l_node));
 dbms_output.put_line('Emp Name: '||l_value);
END LOOP;

-- Method 2
dbms_output.new_line;
dbms_output.put_line('Method 2');
l_nodelist  := dbms_xmldom.getelementsbytagname(l_domdoc, 'name');  -- This doesn't care about namespaces
-- get first item from list, could loop as shown above
l_node      := dbms_xmldom.item(l_nodelist, 0);
l_value    := dbms_xmldom.getnodevalue(dbms_xmldom.getfirstchild(l_node));
dbms_output.put_line('Emp Name: '||l_value);

-- Done with DOMDocument examples, setup for XMLType based examples
dbms_xmldom.freeDocument(l_domdoc);
l_xmltype := XMLTYPE(l_doc);

-- Method 3
dbms_output.new_line;
dbms_output.put_line('Method 3');
l_index := 1;
WHILE l_xmltype.Existsnode('/a:employees/a:emp[' || To_Char(l_index) || ']', l_a_ns) > 0
LOOP
 l_value := l_xmltype.extract('/a:employees/a:emp[' || To_Char(l_index) || ']/a:name/text()', l_a_ns).getStringVal();
 dbms_output.put_line('Emp Name: '||l_value);
 l_index := l_index + 1;
END LOOP;

-- Method 4
dbms_output.new_line;
dbms_output.put_line('Method 4');
l_value := l_xmltype.extract('/a:employees/a:emp[2]/a:name/text()', l_a_ns).getStringVal();
dbms_output.put_line('Emp Name: '||l_value);

-- Method 5
dbms_output.new_line;
dbms_output.put_line('Method 5');
l_index := 1;
WHILE l_xmltype.Existsnode('/a:employees/a:emp[' || To_Char(l_index) || ']', l_a_ns) > 0
LOOP
 l_empx := l_xmltype.extract('/a:employees/a:emp[' || To_Char(l_index) || ']', l_a_ns);
 l_col_ind := 1;
 WHILE l_empx.Existsnode('/a:emp/b:favorites/b:color[' || To_Char(l_col_ind) || ']', l_both_ns) > 0
 LOOP
    l_value := l_empx.extract('/a:emp/b:favorites/b:color[' || To_Char(l_col_ind) || ']/text()', l_both_ns).getStringVal();
    dbms_output.put_line('Color: '||l_value);
    l_col_ind := l_col_ind + 1;
 END LOOP;
 l_index := l_index + 1;
END LOOP;
END;

Running this script produces

Method 1
Emp Name: Scott
Emp Name: John
 
Method 2
Emp Name: Scott
 
Method 3
Emp Name: Scott
Emp Name: John
 
Method 4
Emp Name: John
 
Method 5
Color: red
Color: orange
Color: blue
Color: green

which is exactly the same output as the previous example. This is what we expected. The only call that did not have to change was the one for Method 2. DBMS_XMLDOM is pretty much ignores namespaces when performing operations so this does have useful situations. As Methods 1, 3, and 4 show, the namespace parm only needs to contain the URI information for namespaces referenced in the Xpath, not in the XML. All the namespaces information can be passed along, but it is not needed. Pretty simple, excluding the whole "wait, what namespace is that node in again?" issue.