DomXPath: Search inside DomXPath query result?

Question

How can I query an xpath result for a sub element, without querying the entire document again?

I query my document to find the last <li> with the class menu-item:

$doc = new DomDocument();
@$doc->loadHTML( $html );
// $html is invalid (and should be at this point),
// so use @ sign to suppress errors
$xpath = new DomXPath( $doc );
$li = $xpath->query( "(//li[contains(concat(' ', normalize-space(@class), ' '), 'menu-item')])[last()]" )->item( 0 );

The above works just fine, now I want to query $li to find the following:

$p = $xpath->query( "//p[contains(concat(' ', normalize-space(@class), ' '), 'field-description')]" )->item( 0 );

A p tag with class field-description. This does not work and returns the first instance found, if I modify it and use the [last()] (whatever this is) then it works, but it's not necessarily the optimal solution here:

$p = $xpath->query( "(//p[contains(concat(' ', normalize-space(@class), ' '), 'field-description')])[last()]" )->item( 0 );

The above line works, but I want to query inside $li not the entire document again.

score 3 · Answer 1 · edited May 23 '17 at 12:27

The second argument to query is the contextnode, which limits the search to within that node. However, if you use an absolute xpath, query will still return nodes for the entire document.

php > $dd = new DomDocument();
php > // deliberately using malformed html.
php > $dd->loadhtml('<html><head><title>wat</title></head><body><div>Hello, <p>world</p></div><div class="container"><p>I like pie</div></body></html>');
php > $xp = new DomXPath($dd); 
php > $container = $xp->query('//div[@class="container"]')->item(0);
php > var_dump($xp->query('//p'));
class DOMNodeList#6 (1) {
  public $length =>
  int(2)
}
php > var_dump($xp->query('//p', $container));
class DOMNodeList#4 (1) {
  public $length =>
  int(2)
}
php > var_dump($xp->query('p', $container));
class DOMNodeList#5 (1) {
  public $length =>
  int(1)
}

You can use a pattern like .//x to match all x elements recursively within a context node. (HT: Alf Eaton)

What about when `p` is not a direct child of `.container` in your example. For example, in my html my `p` tag is located in: `div.menu-item-settings` and then in `p.field-description`. My results for searching for `$xpath->query( 'p', $li );` in my example still return 0 results, how can I find `p` within `$li` without knowing the full path within `li`? — Brian Graham, Apr 12 '14 at 05:30

DomXPath: Search inside DomXPath query result?

1 Answers1