Parsing Complex XML Document using PHP xPath

Question

I have an XML Structure, like I have outline below. I am trying to use xPath to find particular elements within the structure, but have been unsuccessful. This is what I have thus far:

$resultset[0]['bibXML'] - Here is a paste of exactly what is being passed in this variable. http://pastebin.com/CwtFG5dj

Here is a link to the output of the $myNode using print_r(). http://pastebin.com/TwDaxs42

$myNode = new SimpleXMLElement($resultset[0]['bibXML']);
$bnum = $myNode->xpath("record/datafield[@tag='035']/subfield[@code='a']");


<?xml version="1.0" encoding="UTF-8"?>
<collection xmlns="http://www.loc.gov/MARC21/slim">
<record>
    <leader>01220nam  2200265   4500</leader>
    <controlfield tag="001">ocm00000197</controlfield>
    <datafield tag="035" ind1="" ind2="">
        <subfield code="a">.b10000021</subfield>
        <subfield code="b">a    </subfield>
        <subfield code="c">-</subfield>
    </datafield>
    <datafield tag="245" ind1="" ind2="">
        <subfield code="a">Some Book Title</subfield>
        <subfield code="b">a    </subfield>
        <subfield code="c">-</subfield>
    </datafield>
</record>
</collection>

Francis Avila · Accepted Answer · 2013-01-23 20:21:34Z

1

Your elements are in the http://www.loc.gov/MARC21/slim namespace. Learn about xml namespaces.

Your XPath is matching elements in the null namespace because they are not prefixed. Since your elements are not actually in the null namespace, your XPath does not match anything.

You need to register a namespace prefix with the registerXPathNamespace method and then use that prefix to qualify your element names.

This would be your complete code:

$myNode = simplexml_load_string($resultset[0]['bibXML']);

$myNode->registerXPathNamespace('m21s', 'http://www.loc.gov/MARC21/slim');

$results = $myNode->xpath('m21s:record/m21s:datafield[@tag="035"]/m21s:subfield[@code="a"]');
$bnum = ($results) ? (string) $results[0] : null;

var_export($bnum);

edited Jan 23, 2013 at 20:21

answered Jan 23, 2013 at 18:45

Francis Avila

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4 Comments

rtd1123 Over a year ago

I have updated my code to your suggestion and I am still not getting a response. Is "New SimpleXMLElement" the correct function to load the xml into?

Francis Avila Over a year ago

Yes, but you can also say simplexml_load_string($xml_string). I've posted the complete code, which works fine for me.

Francis Avila Over a year ago

Yes, it is the problem. Your top-level node is collection, not record, and all nodes are in the http://www.loc.gov/MARC21/slim namespace. Please edit your question to reflect reality!

rtd1123 Over a year ago

Thank you so much, you're a lifesaver, I can't believe that a namespace was the cause of all of this. Thanks again!

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