Throwing an exception from XSLT

Question

Just wanted to share a finding with the Oracle XDB community and possibly suggest an enhancement to the xdb product development team (care of MDRAKE).
I had a scenario where I wanted to throw an exception from the XSLT.
A little Googling revealed this helpful post:
http://weblogs.asp.net/george_v_reilly/archive/2006/03/01/439402.aspx
...so I gave it a shot.
In my XSLT, I have a <xsl:choose> block with the following <xsl:otherwise> block:
<xsl:otherwise>
    <xsl:message terminate="yes">Unknown Document Type</xsl:message>                          
</xsl:otherwise>I used a stub test to run this through, giving it a file which would exercise the exception:
select xmltype(bfilename('XML_RESOURCES', 'data.xml'),0).transform(xmltype(bfilename('XML_RESOURCES', 'sanitize_xml.dev.xsl'),0))
from dual;..and to my 'joy', I did get an exception:
ORA-30998: transformation error: execution of compiled XSLT on XML DOM failedHmm...would of been nicer to get something like what Eclipse/Xalan pops out:
file:/H:/eclipse_indigo_workspace/XSLT/sanitize_xml.xsl; Line #28; Column #59; Unknown Document Type
(Location of error unknown)Stylesheet directed termination...i.e. my custom error message "Unknown Document Type" isn't output by Oracle.
Just to be safe, I tried a file which would NOT exercise this xsl:otherwise block and it did run through OK.
So, could XDB report a better error?
Thoughts?

Answer 1

SQL> VAR XSL VARCHAR2(4000)
SQL> --
SQL> begin
  2    :XSL :=
  3  '<?xml version="1.0" encoding="UTF-8"?>
  4  <xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  5     <xsl:output method="xml" indent="yes"/>
  6     <xsl:template match="/">
  7             <Result>
  8                     <xsl:choose>
  9                             <xsl:when test="Input=''1''">
10                                     <Output>1</Output>
11                             </xsl:when>
12                             <xsl:when test="Input=''2''">
13                                     <xsl:message>The value is 2</xsl:message>
14                                     <Output>2</Output>
15                             </xsl:when>
16                             <xsl:when test="Input=''3''">
17                                     <xsl:message terminate="no">The value is 3</xsl:message>
18                                     <Output>3</Output>
19                             </xsl:when>
20                             <xsl:otherwise>
21                                     <xsl:message terminate="yes">Invalid value</xsl:message>
22                                     <Output>Bad Input</Output>
23                             </xsl:otherwise>
24                     </xsl:choose>
25             </Result>
26     </xsl:template>
27  </xsl:stylesheet>';
28  end;
29  /
PL/SQL procedure successfully completed.
Elapsed: 00:00:00.00
SQL> select XMLTRANSFORM(XMLTYPE('<Input>1</Input>'),XMLTYPE(:XSL))
  2    from dual
  3  /
<?xml version="1.0" encoding="WINDOWS-1252"?>
<Result>
  <Output>1</Output>
</Re
Elapsed: 00:00:00.01
SQL> select XMLTRANSFORM(XMLTYPE('<Input>2</Input>'),XMLTYPE(:XSL))
  2    from dual
  3  /
<?xml version="1.0" encoding="WINDOWS-1252"?>
<Result>
  <Output>2</Output>
</Re
Elapsed: 00:00:00.00
SQL> select XMLTRANSFORM(XMLTYPE('<Input>3</Input>'),XMLTYPE(:XSL))
  2    from dual
  3  /
<?xml version="1.0" encoding="WINDOWS-1252"?>
<Result>
  <Output>3</Output>
</Re
Elapsed: 00:00:00.01
SQL> select XMLTRANSFORM(XMLTYPE('<Input>4</Input>'),XMLTYPE(:XSL))
  2    from dual
  3  /
ERROR:
ORA-30998: transformation error: execution of compiled XSLT on XML DOM failed
no rows selected
Elapsed: 00:00:00.01
SQL>
SQL>The actuall error is not unreasonalbe. The Execution did fail beacuse you terminated it.. Contacting Oralce Support may be a little excessive...
Now with respect to message the question is where...
We 'could' output into the same buffer as is used by DBMS_OUTPUT, but that has limits in terms of the amount of output that can be generated.
We could write it to the trace file, but that may be difficulat for a developer to get to
We could write it to a log file in the XDB repository, but where and how to name it...
We could another parameter to XMLTransform, which would be a Message Buffer
All of these are in effect enhancements..
BTW I checked with XML Spy and they seem to ignore message too, so I'm wondering how widely used this is...
We cannot add it to the output of the XSL since XMLTransform defines the output of the XML to be well formed XML, and adding a random set of text nodes would viloate that rule..