I'm using Magical Record in my app.
I have a relationship...
Competition <-->> League
Competition to League
NSArray *leagues = [League findAll];
for (League *league in *leagues)
NSLog(@"%@ - %@", league.name, league.competition.name);
e.g. Man UTD - Premier League
e.g. Man UTD - (null)
The relationship delete rules are applied when the managed object
context is saved, or
processPendingChanges is called.
As can be seen in the implementation, the MagicalRecord method
deleteObject on all objects of an entity, but does not save the context.