Trying to iterate over a mongodb cursor twice - failing - php

Question

I am executing a query against my mongodb database... and then in two separate spots in my front end logic, I need to iterate through the results to extract / show different information.
Problem
The second time I try to iterate through, I get the following error message:
Fatal error: Uncaught MongoDB\Driver\Exception\LogicException: Cursors
cannot yield multiple iterators in
/var/www/localhost/htdocs/widgets/exception_details.php:46
Stack trace: #0
Backend Code
Here's the logic to query the database in my model:
try{
$id = new \MongoDB\BSON\ObjectId($docid);
$filter = ['_id' => $id];
$options = [];
$query = new \MongoDB\Driver\Query($filter, $options);
$rows = $m->executeQuery('widgets.play_summary', $query);
return $rows;
} catch (Exception $e) {
echo 'Exception:'. $e->getMessage();
return false;
}
Front End Logic
Here's the logic that attempts the iteration.
First time:
foreach ($rows as $id=>$value) {
if ( count($value->unreachable_servers > 0) ) {
foreach($value->unreachable_servers as $key=>$value) {
echo "<tr>";
echo "<td>$value</td>";
echo "</tr>";
}
}
}
And then later, I try to do this:
$it = new IteratorIterator($rows); //line 46
$it->rewind();
foreach ($rows as $id=>$value) {
if ( count($value->failed_plays > 0) ) {
foreach($value->failed_plays as $key=>$value) {
echo "<tr>";
echo "<td>$value</td>";
echo "</tr>";
}
}
}
Additional Information
Commenting out the following lines gives the exact same error, but just on line 48 instead of line 46:
$it = new IteratorIterator($rows);
$it->rewind();
Any tips would be appreciated.
Thanks.
EDIT 1
As a test, I changed the front end code to use rewind and next like this:
$it = new \IteratorIterator($rows);
$it->rewind();
//foreach ($rows as $id=>$value) {
while($value = $it->current()) {
if ( count($value->unreachable_servers > 0) ) {
foreach($value->unreachable_servers as $key=>$value) {
echo "<tr>";
echo "<td>$value</td>";
echo "</tr>";
}
}
$it->next();
}
And for the second loop:
$it = new IteratorIterator($rows);
$it->rewind();
//foreach ($rows as $id=>$value) {
while($value = $it->current()) {
if ( count($value->failed_plays > 0) ) {
foreach($value->failed_plays as $key=>$value) {
echo "<tr>";
echo "<td>$value</td>";
echo "</tr>";
}
}
$it->next();
}
I get the same results. It works the first time but the second time it bombs with the same error message.

Answer 1

Cursor cannot be iterated twice. Fetch it into array, if it fits into memory:
$rows = $m->executeQuery('widgets.play_summary', $query);
return $rows->toArray();
UPDATE
Since the answer still attracts attention 5 years later, there was https://jira.mongodb.org/browse/PHPC-1691 to implement full Iterator interface, not only Traversable.
The implementation does not resolve OPs issue tho.
Technically https://www.php.net/manual/en/class.mongodb-driver-cursor.php does have the rewind method, but it throws an exception Cursors cannot rewind after starting iteration when called after first document was received: https://github.com/mongodb/mongo-php-driver/blob/0960a204b3b60f8a80375abb6390735b95c821f1/src/MongoDB/Cursor.c#L333