in reply to Any help available for a newbie to XML::LibXML?

I started with a couple other XML packages way back when and was never happy. I accidentally discovered LibXML and after fighting through the docs (they actually are pretty good, you just have to read them all front to back and then use them like a function index) I've never been happier. So stick it out, as it were. My Xpath sucks but here's something anyway.

First, there's a good basic tutorial here: Xpath basics. I use that site over and over because their tutorials are straightforward and well organized even when they aren't the deepest/best. Then, this is what I tried just to play around. 

use XML::LibXML;

my $parser = XML::LibXML->new();

my $tree = $parser->parse_fh(*DATA);
my $root = $tree->getDocumentElement;

for my $node ( $root->findnodes("//Device/*/status/text()") )
{
    print $node->nodeValue, $/;
}
# print $root->serialize(1);

__DATA__
<?xml version="1.0" standalone="yes" ?>

<SymCLI_ML>
  <Symmetrix>
    <Symm_Info>
      <symid>000290101935</symid>
    </Symm_Info>
    <Device>
      <Dev_Info>
        <pd_name>Not Visible</pd_name>
        <dev_name>0040</dev_name>
# ...

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To iterate through all the Device childNodes, this sort of thing should be pretty fast. I think there is a native Xpath for getting child nodes too.

for my $node ( $root->findnodes("//Device/*") )
{
    print $node->nodeName, $/;
}

[download]

You could certainly cook up a hash of the nodeNames/Xpath to "your key names" you want and run your Xpath queries with it so that your solution would (human) scale as it would be little more than a configuration based filter.

(update: corrected an extra word and code comment)

Replies are listed 'Best First'.
Re^2: Any help available for a newbie to XML::LibXML?
by wardy3 (Scribe) on Feb 29, 2008 at 22:32 UTC

    Thanks for the reply

    You've given me some things to think about :-) I'll have a play next week at work

[reply]
Re^2: Any help available for a newbie to XML::LibXML?
by wardy3 (Scribe) on Mar 03, 2008 at 08:39 UTC
    Hi again

    I've written a bit more code to test it out and it is very slow doing the findnodes when I'm already at a position in the tree.

    I've written this test script:

    my $parser = XML::LibXML->new();
my $doc    = $parser->parse_file($filename);
my @devinfo = $doc->findnodes('//Device/Dev_Info');

foreach my $devinfo (@devinfo) {
    my($dev) = $devinfo->findnodes('./dev_name');
    print $dev->to_literal, "\n";
}

    [download]

    The first findnodes runs very quickly (< 1 sec) but the one in the loop is a lot slower. But I don't know why. Doesn't it just have to examine the nodes "under" the current devinfo tag?

    Am I doing something wrong with the findnodes call here?

    Thanks, ~ Michael

[reply]
[d/l]

      The only thing that I see from looking at your code that might be responsible would be that

      my($dev) = $devinfo->findnodes('./dev_name');

      [download]

      actually finds many nodes just to throw them all away except for the first. Maybe do it this way to check how many nodes you find:

      my @found_devices = $devinfo->findnodes('./dev_name');
warn "Found " . scalar(@found_devices);
my $dev = $found_devices[0];

      [download]

      But that's just a shot in the dark. Actually looking at your XML, it shouldn't find more than one device.

[reply]
[d/l]
[select]
        Thanks Corion - interesting thought.

        but unfortunately it's only finding 1 at a time. The speed is about 2 per second which is quite atrocious.

        And I agree, it should only find 1 too. I'm guessing there's a fixed overhead for findnodes which would make sense for what I'm seeing

        Anyway, I've got a few more replies to try out :-)
        and maybe it is time to re-visit my old friend XSLT

        Thanks again for the reply - I'll post back any more findings

[reply]

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