Re: Passing data to XML::Twig twig_roots callbacks....?

From: Dustin Suchter <[email protected]>
> I'm having a hard time wrapping my brain around the idea of using
> twig_roots with twig_handlers (specifically so I can pass data back
> and forth) in order to process large XML files. Perhaps I'm missing
> something obvious, and hopefully someone can help!
> 
> I've got a large XML file currently parsed cleanly using twig_roots
> and setting callbacks on various elements:
> 
> my $xmltwigobj = XML::Twig->new(
>     twig_roots => {
>         'Information/Child/Grandchild' => \&get_grandchild_info,
>     }
> );
> 
> sub get_grandchild_info {
>     my ($twig, $element) = @_;
>     #blah blah, do something print-y here
> }
> 
> My problem is that I'd like to store the info I parse via
> get_grandchild_info somewhere useful, where "useful" is not (a) in a
> global or (b) printed somewhere. Specifically, I'd like to pass the
> reference to a DBM::Deep object to get_grandchild_info and have any
> new info added to the existing DBM::Deep object, but really we
> shouldn't need to be specific, I just want something like:
> 
> sub get_grandchild_info_extra {
>     my ($twig, $element, $hash_ref) = @_;
>     #awesomeness
> }
> 
> I found Question 27 at
> http://xmltwig.com/xmltwig/XML-Twig-FAQ.html#Q27 to be pretty spot-on
> for my needs in terms of data passing, but in the end it didn't help
> me since nobody seems to use the twig_roots parsing methodology in
> combination with the 'closures' mentioned there (which smell a lot
> like globals to me anyway...).
> 
> I'd love to see an example of how to modify my code, above, to allow
> me to pass a 3rd argument to my callback subroutine.

sub get_grandchild_info {
	my hash_ref = shift();
	return sub {
     my ($twig, $element) = @_;
     #blah blah, do something print-y here
   }
}

...

my $xmltwigobj = XML::Twig->new(
    twig_roots => {
        'Information/Child/Grandchild' => 
get_grandchild_info(\%DBM_HASH),
    }
);



Sometimes a plain old global is the best solution though.

And sometimes it's better to have a look at a different module. Maybe 
XML::Rules will end up being easier. Though that of course depends on 
your XML and your needs.

XML::Rules will take care of remembering the data for you and if you 
like you can instruct it to store the data of some tag in a DBM::Deep 
hash:


use XML::Rules;
use DBM::Deep;

my $parser = XML::Rules->new(
	start_rules => [
		YourHugeTag => sub {
			my %temp = %{$_[1]};
			tie %{$_[1]}, 'DBM::Deep', $filename;
			%{$_[1]} = %temp;
			1;
		}
	],
	rules => [
		...

(or if the tag doesn't have any attributes you'd be interested in


my $parser = XML::Rules->new(
	start_rules => [
		YourHugeTag => sub {
			tie %{$_[1]}, 'DBM::Deep', $filename;
			# and maybe 
			# %{$_[1]} = (); 
			# to clear the hash
			1;
		}
	],
	rules => [
		...

And now all the data returned by the rules specified for the child 
tabs of YourHugeTag  will be stored in the DBM::Deep and be available 
in $_[1] within the rule specified for YourHugeTag.


Jenda 
===== [email protected] === http://Jenda.Krynicky.cz =====
When it comes to wine, women and song, wizards are allowed 
to get drunk and croon as much as they like.
	-- Terry Pratchett in Sourcery

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