Call to getChildElements() makes the iteration skip steps

[greg0ire]

I'm trying to read an xml file created with mysqldump --xml

The code looks like this :

<?php

        $reader = new \XMLReader();
        $reader->open($this->filename);
        $objects = new \XMLElementIterator($reader, 'row');

        foreach ($objects as $key => $row) {
            echo 'importing row #' . ($key + 1) . PHP_EOL;

            $this->importRow($row, $manager);
        }

The importRow method loops over fields. It looks like this :

        foreach ($row->getChildElements() as $field) {
            $this->setValue(
                $entity,
                $field->getAttribute('name'),
                (string) $field
            );
        }

When I comment out the importRow() call I get the right number of iterations. When I do not, I get half, and only entities with even ids get imported. It is as if the getChildElements() call would make the pointer increase.

Am I using the library wrong ?

[hakre]

Well, it is actually intended to work that way however, as I could reproduce your issue, it's broken. I'm working on a fix, but until then for your scenario, a working variant is to iterate the child elements via SimpleXMLElement:

        foreach ($row->getSimpleXMLElement() as $field) {
            $this->setValue(
                $entity,
                $field['name'],
                (string) $field
            );
        }

This should work equally well for the moment. Let me know if you run into any issues with that.

[greg0ire]

Glad you could reproduce the issue, and thanks a lot for the workaround, I'll try that tomorrow.

[hakre]

well actually it's not really correct to say this is a flaw. getChildElements() is creating an XMLChildElementIterator that one iterates over all child elements then stops.

Because XMLReader is forward only, such a sub-iterator can not find out that it's done until it has moved on to the next (invalid) element.

In your case, that is the next <row> element of the outer iteration already. However as the outer iteration is an independent iterator on it's own and this is a foreach iteration, it moves on to the next <row> element as well. So one element is skipped per each iteration.

I have to check the invalidation decision for the child iterator here. it should be possible to stop at the closing tag. This should prevent the issue.

[greg0ire]

So both iterators are not so independent, if I get this correctly. They seem to share some kind of cursor, don't they ? Thanks for the explanations, it's very interesting.

[greg0ire]

The workaround works like a charm! Thanks again!

[hakre]

Well the "cursor" they share is XMLReader. I could not find time to fix that bug so far. Glad the alternative worked for you. Thank you for reporting this!

[jwundrak]

@hakre, this issue can be closed, because it was resolved by 0.1.11 with skipNextRead-method and without this method in PR #21

[dearsina]

@jwundrak Can you please show me an example of how you can iterate over child (or grand child) nodes without it skipping the parent nodes using skipNextRead? Because I think this issue is still prevalent.