使用 DOMDocument PHP 获取 Xpath 父节点？

Question

I need to get the parent of a particular node in php. I'm using DOMDocument and XPath. My XML is this:

<ProdCategories>
<ProdCategory>

    <Id>138</Id>

    <Name>Parent Category</Name>

    <SubCategories>

        <ProdCategory>

            <Id>141</Id>

            <Name>Category child</Name>

        </ProdCategory>
   </SubCategories>
</ProdCategory>
</ProdCategories>

The php code:

$dom = new DOMDocument();
$dom->load("ProdCategories_small.xml");
$xpath = new DOMXPath($dom);
$nodes = $xpath->query('//ProdCategory/Id[.="141"]/parent::*')->item(0);
print_r($nodes); 

The print is:

 DOMElement Object ( [tagName] => ProdCategory [schemaTypeInfo] => [nodeName] => ProdCategory [nodeValue] => 141 Category child [nodeType] => 1 [parentNode] => (object value omitted) [childNodes] => (object value omitted) [firstChild] => (object value omitted) [lastChild] => (object value omitted) [previousSibling] => (object value omitted)

The [parentNode] is (object value omitted) , why? I would get

    <Id>138</Id>

    <Name>Parent Category</Name>`

Answer 1

The [parentNode] is (object value omitted) , why?

This is because you use the print_r function and it creates such an output ( via an internal helper function of the dom extension ). The line in code which is creating this is:

print_r($nodes);

The string " (object value omitted) " is given by the DOMNode when either print_r or var_dump are used on it. It tells you, that the object value of that field (named parentNode ) is not displayed but omitted.

From that message you could conclude that the field has a value that is an object. A simple check for the class-name could verify this:

echo get_class($nodes->parentNode), "\n"; # outputs  "DOMElement"

Compare that with fields which are an integer or an (empty) string:

[nodeType] => 1
...
[prefix] => 
[localName] => ProdCategory

So I hope this clears it up for you. Just access the field to get the parent node object:

$parent = $nodes->parentNode;

and done.

If you wonder about a certain string that PHP gives you and you have the feeling it might be something internal, you can quickly search all of PHP's codebase on http://lxr.php.net/ , here is an example query for the string in your question .

Answer 2

Just treat the xpath query nodes as filesystem paths, as mentioned here

Move up 2 nodes and get the parent and get what you need from it, such as the Id or Name.

Example:

<?php

$dom = new DOMDocument();
$dom->load("ProdCategories_small.xml");
$xpath = new DOMXPath($dom);

$parentNode = $xpath->query('//ProdCategory[Id="141"]/../..')->item(0);

$id = $xpath->query('./Id', $parentNode)->item(0);
$name = $xpath->query('./Name',$parentNode)->item(0);

print "Id: " . $id->nodeValue . PHP_EOL;
print "Name: " . $name->nodeValue . PHP_EOL;