/**
  * Array access. Get field using external_id or offset.
  */
 public function offsetGet($offset)
 {
     if (is_string($offset)) {
         return $this->get($offset);
     }
     return parent::offsetGet($offset);
 }
 public function offsetSet($offset, $value)
 {
     if (!is_a($value, 'PodioItem')) {
         throw new PodioDataIntegrityError("Objects in PodioItemCollection must be of class PodioItem");
     }
     parent::offsetSet($offset, $value);
 }