PHP / SimpleXML / XPath通过同一元素中的另一个属性获取属性值

Question

I have this XML (from a pptx file):

<Relationships>
    <Relationship Id="rId3" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/image" Target="../media/image2.png"/>
    <Relationship Id="rId2" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/image" Target="../media/image1.wmf"/>
    <Relationship Id="rId1" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/slideLayout" Target="../slideLayouts/slideLayout1.xml"/>
</Relationships>

I want to pull the Target attribute from a Relationship element, and I know the Id value.

I could do it with SimpleXML if I iterate through the nodes (like this question)

$resxml = simplexml_load_file('zip://my.pptx#ppt/slides/_rels/slide1.xml.rels');
echo $resxml->Relationship[0]->attributes()->Target;

But I would like to get it using xpath using this sort of idea. Whatever I do in xpath returns an empty object when I search for something like 'rId3'. I thought it would be the below xpath statement, but it returns an empty object. I have tried about 50 combimations and found a lot of similar but not identical issues when searching:

$image = $resxml->xpath("/Relationships/Relationship[@Id='rId3']/@Target"); 
print_r($image);

I guess I will just end up iterating through all the nodes but it seems inefficient. My server appears to have XPath in the Dom available and SimpleXML enabled.

Answer 1

I think you problem might be the namespace. PPTX Relationship files use the namespace "http://schemas.microsoft.com/package/2005/06/relationships". But SimpleXmls xpath does it's own magic, too. If the file contains the namespace (check the source) you have to register an own prefix for it.

$xml = <<<'XML'
<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>
<Relationships
 xmlns="http://schemas.microsoft.com/package/2005/06/relationships">
 <Relationship Id="rId1"
 Type="http://schemas.microsoft.com/office/2006/relationships/image"
 Target="http://en.wikipedia.org/images/wiki-en.png"
 TargetMode="External" />
 <Relationship Id="rId2"
 Type="http://schemas.microsoft.com/office/2006/relationships/hyperlink"
 Target="http://www.wikipedia.org"
 TargetMode="External" />
</Relationships> 
XML;

$dom = new DOMDocument();
$dom->loadXml($xml);
$xpath = new DOMXpath($dom);
$xpath->registerNamespace('r', 'http://schemas.microsoft.com/package/2005/06/relationships');

var_dump(
  $xpath->evaluate("string(/r:Relationships/r:Relationship[@Id='rId2']/@Target)", NULL, FALSE)
);

Output:

string(24) "http://www.wikipedia.org"

Xpath does not know something like a default namespace. Without a prefix you look for elements without any namespace. Attributes don't have a namespace if not explicitly prefixed.

To make the confusion complete, do the PHP functions (SimpleXMLElement::xpath(), DOMXpath::query() and DOMXpath::evaluate()) automatically register the namespace definitions of the used context. The third argument allows to disable that behaviour.

Unlike the other two functions, DOMXpath::evaluate() can return scalars directly.