Description:
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From manual page: http://www.php.net/mongocollection.remove#refsect1-mongocollection.remove-returnvalues
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If you try to remove() a non-existent record from a collection with 'w' set to 1, remove() doesn't return an error or throw exception.

Instead it returns the array similar to this
Array ( [n] => 0 [connectionId] => 10726 [err] => [ok] => 1 ) 

So now we have to check if [n] is greater than 0 to actually know if remove() succeeded.

Test script:
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$user_id = 'ffffffffffffffffffffffff'; // this doesn't exist in the collection.
$result = $collection->remove(array('_id' => new MongoID($user_id)), array('w' => 1));
print_r($result);



Expected result:
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Array ( [n] => 0 [connectionId] => 10726 [err] => 'some error msg' [ok] => 0 ) 

Actual result:
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Array ( [n] => 0 [connectionId] => 10726 [err] => [ok] => 1 )