the `add()` method seems to actually exist on `DataList` and the `RelationList` subClasses so we should be able to use `$this->gridField->list->add($record->ID);`in all 3 situations (has _one_, many or manymany) saving us a few lines of code. This would be enough then?
`````
$record = Object::create($recordClass);
$record->write();
$this->gridField->list->add($record->ID);
````