in reply to Re: Pulling out sections of an XMI file with XML::Twig
in thread Pulling out sections of an XMI file with XML::Twig

*click* ...a lightbulb turns on...

Thank you for the example code - that made all the difference! I didn't realize that $section was actually an XML::Twig::Elt object. Using your example as a starting point, I was able to get what I needed.

At first I thought I needed to parse the XML chunks into a data structure (such as that returned by XML::Simple), which I accomplished using 

my $struct = $section->simplify( forcearray => 1 );

[download]
but I soon realized that was overkill for what I really needed - the value of the attributes for the class (etc) tags. The $elt->att( $attribute ) method did the trick. An example of the class handler from my working code is below. 
sub uml_class
{
    my ( $twig, $section ) = @_;

    print "data for class:\n";
    print "   name = ", $section->att( 'name' ), "\n";
    print "   xmi.id = ", $section->att( 'xmi.id' ), "\n";

    my $subTwig = XML::Twig->new( twig_roots => {
                                      'UML:Attribute' => \&uml_attr } 
+);
    # $subTwig->parse( $xml ); # original code (typo)
    $subTwig->parse( $section->sprint() );
}

[download]

Thanks again! I knew I was making it too hard. :-)

Update: corrected typo in the example code

Replies are listed 'Best First'.
Re^3: Pulling out sections of an XMI file with XML::Twig
by mirod (Canon) on Sep 28, 2006 at 09:42 UTC

    I must admit that I don't quite understand what you are doing, or even trying to do, but it looks like you are parsing things several time ( the call to parse in uml_class, but I fail to see what's exactly in $xml). It should not be necessary, you can set handlers at different levels of the tree (not twig_roots, but regular twig_handlers).

    If you could repost a complete example I might be able to help.

[reply]

      Thank you for trying to help - I am still very new to XML::Twig and I am probably not doing things as efficiently as I could be. (Sorry for the typo with $xml in the above code - I fixed it.)

      I'm trying to extract certain attributes from a small set of tags in the XML document referenced above. Specifically, the UML:Class tags contain UML:Attribute tags, and I want to extract the name and xmi.id attributes from them. The general structure of this portion of the document looks like this: 

      <UML:Class>
    <UML:Attribute></UML:Attribute>
    <UML:Attribute></UML:Attribute>
    <UML:Attribute></UML:Attribute>
</UML:Class>

      [download]
      A complete example is shown under the readmore.
      Read more... (13 kB)

      If I understand how XML::Twig works, a section of the tree is sent to a handler when the closing tag is reached. Therefore, for the simplified example above, each of the UML:Attribute sections will get parsed before the corresponding UML:Class section is parsed. I would like to parse the Class first (so I don't have to jump through hoops to associate the Attribute data with the Class data later), which is why the handler for UML:Attribute is located in the handler for UML:Class.

      I admit that it seems inefficient to call sprint and then parse. I took that snippet from GrandFather's example. Is there a better way to do it?

      I hope that clarifies what I'm trying to do. I'd appreciate any suggestions that you might have. Thanks.

[reply]
[d/l]
[select]

        2 things can help you here: you can use start_tag_handlers, which are called after the start tag of the element has been parsed (and the element object has been created, empty at that point). This also means taht the UML:Attribute element will get completely parsed before the UML:Class, but when you're in their handler the opening tag of UML:Class has already been parsed. If you don't use twig_roots but regular twig_handlers the element exists, it's an ancestor of the UML:Attribute element, and it's attributes are already available. If space is a problem, you cant sprinkle purge call to taste.

        So in your case I would write something like (untested):

        use strict;
use warnings;

use Data::Dumper;
use XML::Twig;

my $twig = XML::Twig->new(
  start_tag_handlers => { 'UML:Class' => \&ulm_class, }, 
  twig_handlers      => { 'UML:Class' =>  sub { $_[0]->purge }, # purg
+e at the end of each section,
                          'UML:Attribute' => \&uml_attr,
 } );
$twig->parsefile( 'testfile.xmi' );


sub uml_class
{
    my ( $twig, $section ) = @_;

    print "data for class:\n";
    print "   name = ", $section->att( 'name' ), "\n";
    print "   xmi.id = ", $section->att( 'xmi.id' ), "\n";
}


sub uml_attr
{
    my ( $twig, $attr ) = @_;
    # if you need the class id, it's in $attr->parent( ''UML:Class')->
+attr( 'xmi.id')
    $attr->print;

    print Dumper( $struct );
    # parse the block and extract the data elements

    $twig->purge;
}

        [download]

        Does it make sense? It probably doesn't matter that much if your files are small, but it feels better to parse only once each section.

[reply]
[d/l]

In Section Seekers of Perl Wisdom