retrieveData<DataT extends Data> function
retrieves a DataT via its id
and corresponding parentId
Implementation
Future<DataT?> retrieveData<DataT extends Data>(String id,
{required String parentId}) async {
final collectionName = _getCollectionNameForData<DataT>(parentId);
final data = await db.collection(collectionName).doc(id).get();
return Data.fromJson<DataT>(data ?? {});
}