Unable to findnodes() restricted just to current parent - perl-module

Question

I'm parsing a simple XML file to create a flat text file from it. The desired outcome is shown below the sample XML. The XML has sort of a header-detail structure (Assembly_Info and Part respectively), with a unique header node followed by any number of detail record nodes, all of which are siblings. After digging into the elements under the header, I can't then find a way back 'up' to then pick up all the sibling detail nodes.
XML file looks like this:
<?xml version="1.0" standalone="yes" ?>
<Wrapper>
<Record>
<Product>
<prodid>4094</prodid>
</Product>
<Assembly>
<Assembly_Info>
<id>DF-7A</id>
<interface>C</interface>
</Assembly_Info>
<Part>
<status>N/A</status>
<dev_name>0000</dev_name>
</Part>
<Part>
<status>Ready</status>
<dev_name>0455</dev_name>
</Part>
<Part>
<status>Ready</status>
<dev_name>045A</dev_name>
</Part>
</Assembly>
<Assembly>
<Assembly_Info>
<id>DF-7A</id>
<interface>C</interface>
</Assembly_Info>
<Part>
<status>N/A</status>
<dev_name>0002</dev_name>
</Part>
<Part>
<status>Ready</status>
<dev_name>0457</dev_name>
</Part>
</Assembly>
</Record>
</Wrapper>
For each Assembly I need to read the values of the two elemenmets in Assembly_Info which I do successfully. But, I then want to read each of the Part records that are associated with the Assembly. The objective is to 'flatten' the file into this:
prodid id interface status dev_name
4094 DF-7A C N/A 0000
4094 DF-7A C Ready 0455
4094 DF-7A C Ready 045A
4094 DF-7A C N/A 0002
4094 DF-7A C Ready 0457
I'm attempting to use findnodes() to do this, as that's about the only tool I thought I understood. My code unfortunately reads all of the Part records from the entire file foreach Assembly--since the only way I've been able to find the Part nodes is to start at the root. I don't know how to change 'where I am', if you will; to tell findnodes to begin at current parent. Code looks like this:
my $parser = XML::LibXML -> new();
my $tree = $parser -> parse_file ('DEMO.XML');
for my $product ($tree->findnodes ('/Wrapper/Record/Product/prodid')) {
$prodid = $product->textContent();
}
foreach my $assembly ($tree->findnodes ('/Wrapper/Record/Assembly')){
$assemblies++;
$parts = 0;
for my $assembly ($tree->findnodes ('/Wrapper/Record/Assembly/Assembly_Info')) {
$id = $assembly->findvalue('id');
$interface = $assembly->findvalue('interface');
}
foreach my $part ($tree->findnodes ('/Wrapper/Record/Assembly/Part')) {
$parts++;
$status = $part->findvalue('status');
$dev_name = $part->findvalue('dev_name');
}
print "Assembly No: ", $assemblies, " Parts: ",$parts, "\n";
}
How do I get just the Part nodes for a given Assembly, after I've gone down to the Assembly_Info depths? There is quite a bit I'm not getting, and I think a problem may be that I'm thinking of this as 'navigating' or moving a cursor, if you will. Examples of XPath path expressions have not helped me.

Answer 1

Instead of always using $tree as the starting point for the findnodes method, you can use any other node, especially also child nodes. Then you could use a relative XPath expression. For example:
for my $record ($tree->findnodes('/Wrapper/Record')) {
for my $assembly ($record->findnodes('./Assembly')) {
for my $part ($assembly->findnodes('./Part')) {
}
}
}