Mongo-PHP - MongoCursor exception with MongoDB PHP Driver v1.6 - php

Question

I'm having troubles with PHP MongoCursor since I upgraded to Mongo PHP Driver from 1.5.8 to 1.6.0
The following code works well with version 1.5.8, but crashes with version 1.6
PHP version is 5.5.21., Apache version is Apache/2.4.10 (Ubuntu)
$mongoClient = new \MongoClient($serverUrl, ['readPreference'=>\MongoClient::RP_NEAREST]);
$database = $mongoClient->selectDB($dbName);
$collection = $database->selectCollection($collectionName);
// count() works fine and returns the right nb on documents
echo '<br/>count returned '.$collection->count();
// find() exectues with no error...
$cursor = $collection->find();
$documents = [];
// ...and hasNext() crashes with the Excetion below
while($cursor->hasNext()){$documents[] = $cursor->getNext();}
return $documents;
And so the hasNext() call crashes with this message :
CRITICAL: MongoException: The MongoCursor object has not been correctly initialized by its constructor (uncaught exception)...
Am I doing something wrong ?
Thanks for you help !

Answer 1

This may be related to a bug that was introduced in 1.6.0 regarding iteration with hasNext() and getNext(): PHP-1382. A fix has since been merged to the v1.6 branch and should be released later this week as 1.6.1.
That said, the bug regarding hasNext() was actually that the last document in the result set would be missed while iterating. If I run your original script against 1.6.0, the array contains a null value as its last element. With the fix in place, the array will contain all documents as is expected. I cannot reproduce the exception you're seeing with either version.
That exception is actually thrown from an internal checks on the C data structures, to ensure that the cursor object is properly associated with a MongoClient and socket connection. See the MONGO_CHECK_INITIALIZED() macro calls in this file. Most all of the cursor methods check that a MongoClient is associated, but hasNext() is unique in that it also checks for the socket object (I believe other methods just assume a cursor with a MongoClient also has a socket). If that exception is truly reproducible for you and you're willing to do some debugging with the extension, I'd be very interested to know which of the two checks is throwing the error.
As a side note, you should also be specifying the "replicaSet" option when constructing MongoClient. This should have the replica set name, which ensures that the driver can properly ignore connections to hosts that are not a member of the intended replica set.

Answer 2

I just encountered the same issue; I refactored my code to use the cursor iterator instead, ie:
foreach( $cursor as $doc ) {
$documents[] = $doc;
}

Answer 3

I was looking for a code example of how to implement a tailable cursor and found this question. The following code is a simple example of a tailable cursor (via the $cursor variable) which you provide on a capped mongodb collection.
$cursor->tailable(true);
$cursor->awaitData(true);
while (true) {
if ($cursor->hasNext()) {
var_dump($cursor->getNext());
} else {
if ($cursor->dead()) {
break;
}
}
}