此PHP DOM代码有什么问题？

Question

$doc = new DOMDocument();
$doc -> load("state.xml");
...snip...
$neworder = $doc -> createElement("order");
    $neworder -> appendChild($type);

That last line of code is causing the script to fail. 500 HTTP response. If I comment it out, the script runs fine.

get_class() confirms that both $neworder and $type are of the DOMElement class. What could the problem be?

...

On where I'm getting the nodes I'm trying to add:

This is where $type comes from.

for ($i = 0; $i < $ordersummary -> length; $i++)
{
   $o = $ordersummary -> item($i);
   $type = $o -> getElementsByTagName("type") -> item(0);
   ...

and $ordersummary is obtained like this

$ordersummary -> loadXML($_POST["data"]);
$ordersummary = $ordersummary -> getElementsByTagName("order");

Answer 1

The Exception is thrown because you try to append a node from one Document into another. That is not supported by the DOM API.

EDIT: The only sane workaround is to deep-copy the element. Depending on whether or not type is a complex XML structure it may be just a lot easier to serialise the type node to XML string, then create a DOMDocumentFragment for the receiving DOMDocument object and load the raw XML into this DOMDocumentFramgnent. Then you can append the DOMDocumentFragment as you would a DOMElement to insert the type XML data.

Answer 2

As jswolf19 pointed out, you can't append a node coming from a different document, from the documentation:

DOM_WRONG_DOCUMENT_ERR

Raised if newnode was created from a different document than the one that created this node.