[Catalyst] Output as XML

[Mitch Jackson]

Good morning!

I'm about to start working on some DBIC query to XML code, but before
I do I was wondering if anybody out there has already done this, or if
perhaps my approach is thick-headed.

I'm generating XML from database queries in a catalyst app.  At the
moment, I am doing it a bit like this (simplified for readability):

---------------------------------------------------------------------
# controller.pm  /controller/action/parm1/parm2/parm3/something.xml
sub action : Local {
  ...
  $c->stash->{records} = [ $c->model('table')->search( {}, { rows =>
20, page 2 } ) ];
  $c->res->content_type('text/xml');
  $c-.res->header('Content-disposition' => 'attachment;
filename=action_${timestamp}.xml');
  $c->res->template('xml/action.xml');
}

# xml/action.xml
<?xml version="1.0" encoding="utf-8" ?>
<records>
[% FOREACH record IN records -%]
<record id="[% record.id %]">
  <field1>[% record.field1 %]</field1>
  <field2>[% record.field2 %]</field2>
  <field3>[% record.field3 %]</field3>
</record>
[% END # foreach record -%]
</records>
-------------------------------------------------------------------------------

This approach works fine for paged record sets ( that get loaded into
an ExtJS ajax grid ).  When I use this on a record set of 15k-16k
records, the app goes to 100% CPU and cannot complete the request
after several minutes.  There is a lot of overhead to generate 16k
DBIC objects, dump them in an array, and then manipulate them through
TT.

This speed problem is unacceptable for my app, especially considering
my users may be dealing with much larger datasets than this.

One solution would be to write something proprietary to this
implementation as a module that would throw away the overhead bloat
and generate the XML file efficiently... but I want something reusable
in the long term from a catalyst perespective.

I am considering writing some sort of DBIC query to XML code that
would use the DBI cursor directly to bypass object creation and build
the XML while looping through the results.
(http://search.cpan.org/~ash/DBIx-Class-0.08010/lib/DBIx/Class/Manual/Cookbook.pod#Get_raw_data_for_blindingly_fast_results)

An interface like this:
my $xml = $c->model('table')->xml( \%filter_parms, \%dbic_opts )

That would generate output like this
<?xml version="1.0" encoding="utf-8" ?>
<records>
<record id="42">
  <field1>don't panic</field1>
  <field2>vogon poetry</field2>
  <field3>see if i don't</field3>
</record>
...
</records>

The questions I pose are this:
- Is there something already out there that does what I need?
- Is there a big problem with my approach?
- Would anybody else be interested in this if I get it working?


Kind Regards,

/Mitchell K. Jackson