Phalcon Many to Many relation sync

/**
 * Sync a many to many record to an entity
 * https://laravel.com/docs/4.2/eloquent#inserting-related-models
 *
 * Usage:
 * $entity->sync('alias_name', array(1, 2, 3), $transaction);
 * @param $related_alias   string   Many to Many alias name
 * @param $identifiers     array    array of ID's of the related records
 * @param $transaction     object   Phalcon Trancation object if the entity is part of a transaction
 * @return true | Exception
 */
public function sync($related_alias, array $identifiers, \Phalcon\Mvc\Model\Transaction $transaction = NULL) {
    $modelsmanager = $this->getDI()->getModelsManager();
    $relation = $modelsmanager->getRelationByAlias(get_class($this), $related_alias);
    if(!$relation) {
        $msg = sprintf('Relation alias "%s" does not exists', $related_alias);
        if($transaction) {
            $transaction->rollback($msg);
        } else {
            throw new \Exception($msg);
        }
    }

    $related_ids = array();
    $existing_ids = array();
    $new_ids = array();

    $related = $this->getRelated($related_alias);
    foreach($related as $r) {
        array_push($related_ids, $r->id);
    }

    foreach($identifiers as $i) {
        if(!in_array($i, $related_ids)) {
            array_push($new_ids, $i);
        } else {
            array_push($existing_ids, $i);
        }
    }

    $delete_ids = array_diff($related_ids, array_merge($existing_ids, $new_ids));

    $intermediate_model = $relation->getIntermediateModel();
    foreach($new_ids as $related_id) {
        $intermediate = new $intermediate_model;
        if($transaction) {
            $intermediate->setTransaction($transaction);
        }
        $intermediate->{$relation->getIntermediateFields()} =  $this->id;
        $intermediate->{$relation->getIntermediateReferencedFields()} = $related_id;
        if($intermediate->create() == false) {
            $msg = 'Could not create intermediate record: ';
            foreach($intermediate->getMessages() as $m) {
                $msg .= $m;
            }
            if($transaction) {
                $transaction->rollback($msg);
            } else {
                throw new \Exception($msg);
            }
        }
    }

    foreach($delete_ids as $related_id) {
        $intermediate = $intermediate_model::findFirst(array(
            $relation->getIntermediateFields().' = ?0 AND '.$relation->getIntermediateReferencedFields().' = ?1',
            'bind' => array(
                0 => $this->id,
                1 => $related_id
            )
        ));
        if($intermediate) {
            if($transaction) {
                $intermediate->setTransaction($transaction);
            }
            if($intermediate->delete() == false) {
                $msg = 'Could not delete intermediate record: ';
                foreach($intermediate->getMessages() as $m) {
                    $msg .= $m;
                }
                if($transaction) {
                    $transaction->rollback($msg);
                } else {
                    throw new \Exception($msg);
                }
            }
        }
    }
    return true;
}