NSFetchedResultsController that contains objects from a relation

Question

I have a NSManagedObject with related objects. The relation is described by a keyPath.

Now I want to display these related objects in a table view. Of course I could just take the NSSet with these objects as a data source, but I'd prefer to refetch the objects with a NSFetchedResultsController to benefit from its features.

How can I create a predicate that describes these objects?

Answer 1

To display the related objects of a given object with a fetched results controller, you would use the inverse relationship in the predicate. For example:

To display the children related to a given parent, use a fetched results controller with the following fetch request:

Parent *theParent = ...;
NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"Child"];
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"parent = %@", theParent];
[request setPredicate:predicate];

For nested relationships, just use the inverse relationships in inverted order. Example:

To display the streets of a given country:

Country *theCountry = ...;
NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"Street"];
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"city.country = %@", theCountry];
[request setPredicate:predicate];