Perl LibXML findvalues(…) concatenates values

Question

I am trying to extract node values from an XML file using LibXML. When I call findvalue all of the nodes of the same element type are concatenated. I am totally

Answer 1

Change the XPaths as follows:

//playlists/dict        →  /playlists/dict
./string                →  key[text()="Name"]/following-sibling::*[1]
//playlists/dict/array  →  key[text()="Playlist Items"]/following-sibling::*[1]/*
./dict/integer          →  key[text()="Track ID"]/following-sibling::*[1]

Yeah, those XPaths are pretty messy, but that's because we're dealing with a horrible schema.

Fixed:

use strict;
use warnings;
use feature qw( say );

use XML::LibXML qw( );

my $doc = XML::LibXML->load_xml( location => $ARGV[0] );

my @playlist_nodes = $doc->findnodes('/playlists/dict');
for my $playlist_idx (0..$#$playlist_nodes) {
   my $playlist_node = $playlist_nodes->[$playlist_idx];

   say "" if $playlist_idx;

   my $name = $playlist_node->findvalue('key[text()="Name"]/following-sibling::*[1]');
   say $name;

   for my $track_node ($playlist_node->findnodes('key[text()="Playlist Items"]/following-sibling::*[1]/*')) {
      my $id = $track_node->findvalue('key[text()="Track ID"]/following-sibling::*[1]');
      say $id;
   }
}

---

Above, I mentioned that the schema being used is horrible. Whoever designed that XML schema was told to use XML, but clearly didn't understand XML. It's bad even for a schema to encode arbitrary data structures like JSON. (This would be better.) Whoever designed it only intended for the data to be converted into a different format before being used. The following does this:

use strict;
use warnings;
use feature qw( say state );

use Carp              qw( croak );
use Types::Serialiser qw( );
use XML::LibXML       qw( );


sub qname {
   my ($node) = @_;
   my $ns   = $node->namespaceURI();
   my $name = $node->nodeName();
   return defined($ns) ? "{$ns}$name" : $name;
}

sub deserialize_array {
   my ($array_node) = @_;
   return [ map { deserialize_value($_) } $array_node->findnodes("*") ];
}

sub deserialize_dict {
   my ($dict_node) = @_;

   my $dict = {};
   my @children = $dict_node->findnodes("*");
   while (@children) {
      my $key_node = shift(@children);
      qname($key_node) eq "key"
         or croak("Expected key");

      my $val_node = shift(@children)
         or croak("Expected value");

      my $key = $key_node->textContent();
      my $val = deserialize_value($val_node);
      $dict->{$key} = $val;
   }

   return $dict;
}

sub deserialize_value {
   my ($val_node) = @_;

   state $deserializers = {
      string  => sub { $_[0]->textContent() },
      integer => sub { 0 + $_[0]->textContent() },
      true    => sub { $Types::Serialiser::true },
      false   => sub { $Types::Serialiser::false },
      array   => \&deserialize_array,
      dict    => \&deserialize_dict,
   };

   my $val_type = qname($val_node);
   my $deserializer = $deserializers->{$val_type}
      or croak("Unrecognized value type \"$val_type\"");

   return $deserializer->($val_node);
}

sub deserialize_doc {
   my ($doc) = @_;
   return deserialize_array($doc->documentElement());
}

With the above, the solution becomes the following:

my $doc = XML::LibXML->load_xml( location => $ARGV[0] );
my $playlists = deserialize_doc($doc);

for my $playlist_idx (0..$#$playlists) {
    my $playlist = $playlists->[$playlist_idx];

    say "" if $playlist_idx;

    my $name = $playlist->{"Name"};
    say $name;

    for my $track (@{ $playlist->{"Playlist Items"} }) {
       my $id = $track->{"Track ID"};
       say $id;
    }
}

Answer 2

Your input data is not easy to process as was indicated by other posters.

Your code could be as following with provided sample of input data.

use strict;
use warnings;
use feature 'say';

use XML::LibXML;

my $playlistxml = 'playlist.xml';

my $dom = XML::LibXML->load_xml(location => $playlistxml);

foreach my $title ($dom->findnodes('//playlist')) {
    say 'Title: ', $title->findvalue('./title');
    my $tracks = join "\n", map {
        $_->to_literal();
    } $title->findnodes('./tracks/track/@id');
    say $tracks;
    say '';
}

Sample of input data 'playlist.xml'

<playlists>
    <playlist id="67312">
        <title>Yes - Tales From Topographic Oceans</title>
        <persistent_id>F28F195257143396</persistent_id> 
        <tracks> 
            <track id="25912" />
            <track id="25914" />
            <track id="25916" />
            <track id="25918" />
        </tracks>
    </playlist>
    <playlist id="67319">
        <title>Yes - Yessongs</title>
        <description>Live Album</description>
        <persistent_id>405B144877D8B8E4</persistent_id>
        <tracks>
            <track id="25920" />
            <track id="25922" />
            <track id="25924" />
            <track id="25926" />
            <track id="25928" />
            <track id="25930" />
        </tracks>
    </playlist> 
</playlists>

Output

Title: Yes - Tales From Topographic Oceans
25912
25914
25916
25918

Title: Yes - Yessongs
25920
25922
25924
25926
25928
25930