lib/components/dataInterface/connectors/file/DataItem.php
protected function fillRelationConfig(&$config, $otherObject)
    {
        if (isset($config['parent_object_id'])) {
            $config['child_object_id'] = $otherObject;
        } elseif (isset($config['child_object_id'])) {
            $config['parent_object_id'] = $otherObject;
        }
    }
protected function fillRelationConfig(&$config, $otherObject)
    {
        if (isset($config['parent_object_id'])) {
            $config['child_object_id'] = $otherObject;
        } elseif (isset($config['child_object_id'])) {
            $config['parent_object_id'] = $otherObject;
        }
    }
fill absent relation attributes.

@param array      $config      relationship configuration
@param Model $otherObject the other object to fill in the relation config data