如何“刷新" LibXML2的DOMDocument实例? [英] How to "refresh" DOMDocument instances of LibXML2?
问题描述
使用PHP进行说明:normalizeDocument()方法中存在一个BUG，或者缺少刷新"方法，因为更改后DOM一致性丢失(甚至只有属性更改). ..因此，您使用LIBXML2 somethimes实现的任何具有DOM更改的算法"都是可行的，有时甚至是无法预测的！ (?)
Using PHP to illustrate: there are a BUG in the normalizeDocument() method, or a lack of a "refresh" method, because DOM consistence is lost after changes (even only attribute changes)... So, any algorithm "with DOM changes" that you implement with LIBXML2 somethimes works and sometimes not, is unpredictable!! (?)
$doc->LoadXML($doc->saveXML());的刷新"是一种变通方法，并且在使用DOM的工作流程中失去了性能...一个子问题:我需要刷新DOM的所有时间吗?
The "refresh" by $doc->LoadXML($doc->saveXML()); is a workaround and lost performance in a flow of work with DOM... A sub-question: all moment I need to refresh DOM?
$XML = '
<html>
<h1>Hello</h1>
<ol>
<li>test (no id)</li>
<li xml:id="i2">test i2</li>
</ol>
</html>
';
$doc = new DOMDocument;
$doc->LoadXML($XML);
doSomeChange($doc); // here DOM is modified
print $doc->saveXML(); // show new DOM state
$doc->normalizeDocument(); // NOT REFRESHING!?!
var_dump($doc->getElementById('i2')); //NULL!??! is a BUG!
//CAN_NOT_doMORESomeChange($doc);
$doc->LoadXML($doc->saveXML()); // only way to refresh?
print $doc->getElementById('i2')->tagName; //OK, is there
// illustrating attribute modification:
function doSomeChange(&$dom) {
$max = 0;
$xp = new DOMXpath($dom);
foreach(iterator_to_array($xp->query('/html/* | //li')) as $e) {
$max++;
$e->setAttribute('xml:id',"i$max");
}
print "\ncmpDOM='".($xp->document === $dom)."'\n"; // after @ThomasWeinert
}
所以，输入是$ XML，输出是
So, input is the $XML and output is
<html>
<h1 xml:id="i1">Hello</h1>
<ol xml:id="i2">
<li xml:id="i3">test (no id)</li>
<li xml:id="i4">test i2</li>
</ol>
</html>
NULL
ol
NULL是错误(请参见代码注释).
the NULL is the bug (see code comments).
PS:如果我将输入线<li xml:id="i2">test i2</li>更改为<li>test i2</li>，则该算法将按预期运行(！)，因此是不可预测的.
PS: if I change input line <li xml:id="i2">test i2</li> to <li>test i2</li> the algorithm works as expected (!), so, is unpredictable.
相关问题:在DomDocument中，DOMXpath的重用是否稳定? PHP DomDocument，可重复使用XSLTProcessor，它稳定/安全吗?
推荐答案
所做的更改将立即应用于DOM.在您的示例中，这将创建一个状态，其中两个元素具有相同的xml:id，这似乎使索引搞砸了.在设置它们之前，请删除xml:id属性，它会起作用:
Changes are applied to the DOM the moment you're doing them. In your example this creates a status where two elements have the same xml:id and this seems to screw up the index. Remove the xml:id attributes before setting them and it works:
$XML = '
<html>
<h1>Hello</h1>
<ol>
<li>test (no id)</li>
<li xml:id="i2">test i2</li>
</ol>
</html>
';
$doc = new DOMDocument;
$doc->loadXML($XML);
var_dump($doc->getElementById('i2'), $doc->getElementById('i2')->tagName);
/*
object(DOMElement)#2 (0) { }
string(2) "li"
*/
doSomeChange($doc); // here DOM is modified
var_dump($doc->getElementById('i2'), $doc->getElementById('i2')->tagName);
/*
object(DOMElement)#6 (0) { }
string(2) "ol"
*/
print $doc->saveXML(); // show new DOM state
/*
<?xml version="1.0"?>
<html>
<h1 xml:id="i1">Hello</h1>
<ol xml:id="i2">
<li xml:id="i3">test (no id)</li>
<li xml:id="i4">test i2</li>
</ol>
</html>
*/
// illustrating xml:id attribute modification:
function doSomeChange($dom) {
$xp = new DOMXpath($dom);
foreach($xp->evaluate('//*') as $e) {
$e->removeAttribute('xml:id');
}
$max = 0;
foreach($xp->evaluate('/html/*|//li') as $e) {
$max++;
$e->setAttribute('xml:id',"i$max");
}
}
您对dom的特定修改是中断getElementById()调用的原因.
Your specific dom modification is, what breaks the getElementById() calls.
对于稳定性"问题:DOMXpath和DOMDocument之间的连接不是完全稳定"的.如果在DOMDocument中使用load *()方法，则连接会丢失.您可以通过比较其文档属性来验证DOMXpath是否使用了正确的DOMDocument:
To the "stability" question: The connection between DOMXpath and DOMDocument is not completly "stable". If you're using a load*() method in the DOMDocument, the connection is lost. You can validate that the DOMXpath uses the correct DOMDocument comparing its document property:
var_dump($xpath->document === $doc);
这种情况不会发生，因为您总是在函数中创建DOMXpath的新实例.但这意味着您应该避免重新加载文档，因为这会破坏为文档创建的xpath实例.
This does not happen in your case, because you always create a new instance of DOMXpath in the function. But it means you should avoid reloading the document because this will break xpath instances created for the document.
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