Un-nest XML with single child element

Question

I'm trying to write a generic function for un-nesting child nodes where nesting is deemed unnecessary. Typically when the element only has one child element.
For example, given the following source....
<ROOT>
  <ITEM>
    <DESCRIPTION>TEST1</DESCRIPTION>
  </ITEM>
  <ITEM>
    <DESCRIPTION>TEST2</DESCRIPTION>
  </ITEM>
</ROOT>I actually want.....
<ROOT>
  <DESCRIPTION>TEST1</DESCRIPTION>
  <DESCRIPTION>TEST2</DESCRIPTION>
</ROOT>because we think ITEM isn't really required before we deliver XML data.
I've been trying to achieve this with a function, where I pass in the XPath to the node I want flattening, something like
function UnNest(pXMLData XMLType, pXPath varchar2) return XMLType...Called like the following...
declare
begin
  vXMLData := UnNest(SomeXMLData, '/ROOT/ITEM')
end;I tried using XQuery Update (11gR2), as follows,
select /*+ no_xml_query_rewrite */
  xmlquery('
    copy $d := .
     modify (
        for $i in $d/ROOT/ITEM
        return
          replace node $i with $i/child::node()  
     return $d'
  passing xmltype(
'<ROOT>
  <ITEM>
    <DESCRIPTION>TEST1</DESCRIPTION>
  </ITEM>
  <ITEM>
    <DESCRIPTION>TEST2</DESCRIPTION>
  </ITEM>
</ROOT>'
  returning content) XML
from dual.... which works, but when I try to pass in a path variable, it doesn't.
select /*+ no_xml_query_rewrite */
  xmlquery('
    copy $d := .
     modify (
        for $i in $d/$Unnestpath
        return
          replace node $i with $i/child::node()  
     return $d'
  passing xmltype(
'<ROOT>
  <ITEM>
    <DESCRIPTION>TEST1</DESCRIPTION>
  </ITEM>
  <ITEM>
    <DESCRIPTION>TEST2</DESCRIPTION>
  </ITEM>
</ROOT>'
  'ROWSET/ROW' as "Unnestpath"
  returning content) XML
from dual
ORA-19112: error raised during evaluation:
XVM-01020: [XPTY0020] The path step context item is not a node
6             replace node $i with $i/child::node()  
-                                   ^Am I missing something obvious?
My destination platform is 11gR2 64 bit but going forward I may need a solution for 10gR2 too. Perhaps there is another way without using XQuery Update? Any advice would be greatly appreciated.

Answer 1

paul zip wrote:
when I try to pass in a path variable, it doesn't.Yes, paths are not variables, they have to be static. However, you can make the whole query dynamic.
Another option is XSLT, which will work on both releases, or a combination of extract/updatexml calls.
SQL> create or replace function UnNest(pXMLData XMLType, pXPath varchar2)
  2  return XMLType
  3  is
  4    result          XMLType;
  5    xsl_template    varchar2(2000) :=
  6    '<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  7    <xsl:template match="@*|node()">
  8      <xsl:copy>
  9        <xsl:apply-templates select="@*|node()"/>
10      </xsl:copy>
11    </xsl:template>
12    <xsl:template match="#TARGET_XPATH#">
13      <xsl:apply-templates select="node()"/>
14    </xsl:template>
15  </xsl:stylesheet>';
16 
17  begin
18 
19    select xmltransform(
20             pXMLData
21           , xmlparse(document replace(xsl_template, '#TARGET_XPATH#', pXPath))
22           )
23    into result
24    from dual ;
25 
26    return result;
27 
28  end;
29  /
Function created
SQL> set long 5000
SQL>
SQL> select unnest(
  2  xmltype(
  3  '<ROOT>
  4    <ITEM>
  5      <DESCRIPTION>TEST1</DESCRIPTION>
  6    </ITEM>
  7    <ITEM>
  8      <DESCRIPTION>TEST2</DESCRIPTION>
  9    </ITEM>
10  </ROOT>'),
11  '/ROOT/ITEM'
12  )
13  from dual;
UNNEST(XMLTYPE('<ROOT><ITEM><D
<ROOT>
<DESCRIPTION>TEST1</DESCRIPTION>
<DESCRIPTION>TEST2</DESCRIPTION>
</ROOT>
Typically when the element only has one child element.If it's a general rule to apply, XSLT can do it very easily on every node that satisfies this condition.
Edited by: odie_63 on 21 mai 2013 12:38