XPath query with PHP

问题:

Here's the XML code I'm working with:

<inventory>     <drink>         <lemonade supplier="mother" id="1">             <price>$2.50</price>             <amount>20</amount>         </lemonade>         <lemonade supplier="mike" id="4">             <price>$3.00</price>             <amount>20</amount>         </lemonade>         <pop supplier="store" id="2">             <price>$1.50</price>             <amount>10</amount>         </pop>     </drink> </inventory> 

Then I wrote a simple code to practice working with XPath:

<?php     $xmldoc = new DOMDocument();     $xmldoc->load('sample.xml');      $xpathvar = new Domxpath($xmldoc);      $queryResult = $xpathvar->query('//lemonade/price');     foreach($queryResult as $result) {         echo $result->textContent;     } ?> 

That code is working well, outputting all the lemonade price values as expected. Now when i change the query string to select only the elements with an attribute set to a certain value, like

//lemonade[supplier="mother"]/price

or

//lemonade[id="1"]/price

it won't work, no output at all. What am i doing wrong?

回答1:

Try this:

//lemonade[@id="1"]/price 

or

//lemonade[@supplier="mother"]/price 

Without the "@" it looks for child elements with that name instead of attributes.

回答2:

This is only tangentially related, but when you use XPath on a document for which you know the structure, don't use "//some-element-name". It's very nice for a quick example, but when you hit a huge xml file with that query, particularly if it is followed by something complex, you will quickly run into performance issues.

inventory/drink/lemonade[@supplier="mother"]/price

回答3:

you have to use the @ sign to indicate attribute within the predicate like so: //lemonade[@supplier="mother"]/price, that's all.

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