SQL -> XML Conversion

set_uk has asked for the wisdom of the Perl Monks concerning the following question:

I am trying to convert Oracle SQL query output to XML. I'm sure someone has tackled this issue previous to me.

I am using the following code to write an XML file:-

   $SelectStatement=$SQL->get($StmntTsk{Def},$StmntTsk{Args}) or throw
TNBCriticalException("Cannot get SELECT SQL from Phrasebook");
    my $XmlOutFile = $fqd_runlogdir.$MSTR::DLM.$StmntTsk{XMLOutput};
    my $ya = XML::Handler::YAWriter->new(AsFile => $XmlOutFile);
    my $generator = XML::Generator::DBI->new(
                        Handler => $ya, 
                        dbh => $dbh,
                        ShowColumns => True
                        );
    $generator->execute($SelectStatement);
[download]

Problem is when I have NULL entries in a database column I get no XML element - when what I want is an empty element. This is because I sometimes want to manipulate the XML into CSV and to have it formatted correctly it needs a comma for each NULL - which I cant do unless I can process a Node in the nodeset via XSL.

Now I know I could change my SQL to wrap these columns with NVL but I thought there might be a way with DBD/Perl to process the NULL's and maintain the elements

Comment on SQL -> XML Conversion Download Code

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Re: SQL -> XML Conversion by mirod (Canon) on Apr 09, 2003 at 08:49 UTC
It seems to me that you could patch XML::Generator::DBI. line 122 is: `$proxy->send_tag($names->[$i], $row[$i], 3) if defined($row[$i]);` A quick fix (untested!), that would work just for you would be to replace this by: `if( defined($row[$i])) { $proxy->send_tag($names->[$i], $row[$i], 3); } else { $proxy->send_tag($names->[$i], '', 3); }` [download] An even better fix would be to add an option in the `new` that would control whether SAX events are emitted or not for a NULL column. Then send the patch to matts and make his day ;--) Update: fixed the code (added brackets around the test). Thanks to gmax who tested it.	[reply] [d/l] [select]
Re: SQL -> XML Conversion by dakkar (Hermit) on Apr 09, 2003 at 15:54 UTC
There is a very good reason for the current behaviour: `NULL` gets mapped to no element, empty string gets mapped to empty element. If you really need to confuse the two concepts, you can write a SAX filter (put it between the generator and your consumer) which fills in the missing elements. On a side note: if you need a CSV, why are you passing through XML? -- dakkar - Mobilis in mobile Most of my code is tested... Perl is strongly typed, it just has very few types (Dan)	[reply]
Re: Re: SQL -> XML Conversion by set_uk (Pilgrim) on Apr 09, 2003 at 22:06 UTC
I agree it appears confused. My theory was to query the db once - convert to XML then use multiple XSLT passes to build whatever output format I needed be it HTML, CSV or different XML format. It works ok - but the important thing is that I now know a hell of a lot more than when I started	[reply]
Re: Re: Re: SQL -> XML Conversion by bronto (Priest) on Apr 10, 2003 at 08:15 UTC
If you need them to be distributed by a web server, you could give AxKit a try. AxKit comes with the AxKit::XSP::ESQL taglib that you could use to query the database and output XML at your pleasure -which you could them make available as an HTML page or whatever format you like. If you are interested in AxKit and the ESQL taglib you could also take a look at this article: Fun with ESQL. Ciao! `--bronto` The very nature of Perl to be like natural language--inconsistant and full of dwim and special cases--makes it impossible to know it all without simply memorizing the documentation (which is not complete or totally correct anyway). --John M. Dlugosz	[reply]


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