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POIn DomDocument, reuse of DOMXpath, it is stable?
 

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  1. POIn DomDocument, reuse of DOMXpath, it is stable?
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    <p>I am using the function below, but not sure about it is always stable/secure... <strong>Is it?</strong> </p> <p><strong>When and who is stable/secure to "reuse parts of the DOMXpath preparing procedures"?</strong></p> <p>To simlify the use of the <a href="http://www.php.net/manual/en/domxpath.query.php" rel="nofollow noreferrer">XPath query() method</a> we can adopt a function that memorizes the last calls with static variables,</p> <pre class="lang-php prettyprint-override"><code> function DOMXpath_reuser($file) { static $doc=NULL; static $docName=''; static $xp=NULL; if (!$doc) $doc = new DOMDocument(); if ($file!=$docName) { $doc-&gt;loadHTMLFile($file); $xp = NULL; } if (!$xp) $xp = new DOMXpath($doc); return $xp; // ??RETURNED VALUES ARE ALWAYS STABLE?? } </code></pre> <hr> <p>The present question is similar to <a href="https://stackoverflow.com/q/18086094/287948">this other one</a> about XSLTProcessor reuse. In both questions the problem can be generalized for any language or framework that use LibXML2 as DomDocument implementation. </p> <p>There are another related question: <a href="https://stackoverflow.com/q/20114285/287948">How to &quot;refresh&quot; DOMDocument instances of LibXML2?</a></p> <hr> <h2>Illustrating</h2> <p>The reuse is very commom (examples):</p> <pre><code> $f = "my_XML_file.xml"; $elements = DOMXpath_reuser($f)-&gt;query("//*[@id]"); // use elements to get information $elements = DOMXpath_reuser($f)-&gt;("/html/body/div[1]"); // use elements to get information </code></pre> <p>But, if you do something like <code>removeChild</code>, <code>replaceChild</code>, etc. (example),</p> <pre><code> $div = DOMXpath_reuser($f)-&gt;query("/html/body/div[1]")-&gt;item(0); //STABLE $div-&gt;parentNode-&gt;removeChild($div); // CHANGES DOM $elements = DOMXpath_reuser($f)-&gt;query("//div[@id]"); // INSTABLE! !! </code></pre> <p><strong>extrange things can be occur</strong>, and the queries not works as expected!!</p> <ul> <li><strong>When</strong> (what DOMDocument methods affect XPath?) </li> <li><strong>Why</strong> we can not use something like <a href="http://www.php.net/manual/en/domdocument.normalizedocument.php" rel="nofollow noreferrer">normalizeDocument</a> to "refresh DOM" (exist?)?</li> <li>Only a "new DOMXpath($doc);" is allways secure? need to reload $doc also?</li> </ul>
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    1. USPeter Krauss
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    1. CODo mean "stable" in the meaning of "read only"? Why should that be? DOMDocument is to read, modify and create XML documents.
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    2. COStable as "work as expected", "no bug", "no surprise". DOMDocument not have a property to say *"the DOM map is lost, must be refreshed"* when you create or modify nodes: some modifications affect DOM, some no. Example: in a loop for traversing DOM, I not have problems with `setAttribute` method, but in general have with `replaceChild`.
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