Core Data在Swift中添加数据。

I'm trying to add this instance of serie to a country via a core-data relation. The only problem is that my NSOrderedSet gets very big and this method of adding gets inefficient because I have to load the whole NSOrderedSetthat already exists (way to big) into memory. Than duplicate it into a editable copy, add the new instance. Than set the large NSOrderedSet the new OrderdSet for that country and save it. (This is by the way a simple solution that I found on the internet)I'm trying to add this instance of serie to a c