使用PHP将XML模式默认注入到文档中

Question

Here we have a simple XML schema:

<xs:schema elementFormDefault="qualified" xmlns:xs="http://www.w3.org/2001/XMLSchema">
    <xs:element name="item">
        <xs:complexType>
            <xs:sequence>
                <xs:element ref="item" minOccurs="0" maxOccurs="unbounded" />
            </xs:sequence>
            <xs:attribute name="is-foo" type="xs:boolean" default="true" use="optional" />
            <xs:attribute name="is-bar" type="xs:boolean" default="false" use="optional" />
        </xs:complexType>
    </xs:element>
</xs:schema>

Just recursive <item> nodes with optional is-foo/is-bar boolean attributes, defaulting to true and false respectively.

Now, how are these default values useful, in the context of reading XML data in PHP? If I have a valid XML document:

<item is-foo="false" is-bar="false">
    <item is-bar="true">
        <item>
            <item is-foo="true">
                <item />
                <item is-foo="true" />
            </item>
        </item>
        <item is-foo="true" is-bar="true" />
    </item>
</item>

Against which I run:

$document = new DOMDocument();
$document->load('./test.xml');
var_dump($document->schemaValidate('./test.xsd'));

$xpath = new DOMXPath($document);
foreach ($xpath->query('//item') as $item) {
    echo $item->getNodePath() . PHP_EOL
        . '  is-foo : ' . $item->getAttribute('is-foo') . PHP_EOL
        . '  is-bar : ' . $item->getAttribute('is-bar') . PHP_EOL;
}

I get the following output (which, while expected, is unfortunate):

bool(true)
/item
  is-foo : false
  is-bar : false
/item/item
  is-foo :
  is-bar : true
/item/item/item[1]
  is-foo :
  is-bar :
/item/item/item[1]/item
  is-foo : true
  is-bar :
/item/item/item[1]/item/item[1]
  is-foo :
  is-bar :
/item/item/item[1]/item/item[2]
  is-foo : true
  is-bar :
/item/item/item[2]
  is-foo : true
  is-bar : true

The issue here being all of the empty attribute values.

Aside from programatically injecting default values into the documents (which would require interpreting the schema for any reusability) are there any options to transform an XML document to include default values as defined in the corresponding schema?

Answer 1

This is not currently possible with the DOM extension.

libxml doesn't do this unless the XML_SCHEMA_VAL_VC_I_CREATE is set on the schema validation context in use, and currently it isn't.

I've created a patch that should hopefully expose this functionality by means of an additional $flags argument to schemaValidate()/schemaValidateSource() and an new LIBXML_SCHEMA_CREATE constant (example target code), but I've yet to test it as I don't have a usable build environment readily available.

EDIT

The patch has now been tested and I've created a PR to merge into the 5.5 branch.

EDIT 2

The PR has now been merged into master and the feature should be available from PHP 5.5.2.

EDIT 3

See it working