By doing this we can, call 'sort', 'skip', 'limit' and others after calling 'where'. Because the mongodb library's MongoDB\Cursor is much more limited (in that regard) than the old driver MongoCursor.
Inheritance: implements Mongolid\Cursor\CursorInterface, implements Serializabl\Serializable
 /**
  * Serializes this object. Drops the unserializable DriverCursor. In order
  * to make the CacheableCursor object serializable.
  *
  * @return string Serialized object.
  */
 public function serialize()
 {
     $this->documents = $this->cursor = null;
     return parent::serialize();
 }