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Question

I am new to Core Data programming and am trying to work out the concepts involved. I have an object called a Lease that has a many-to-many relationship with Apartment objects. Given a Lease object, how do I get a count of the related Apartment objects or an NSArray of the related objects?

Thank you!

~~Garth

Answer 1

There are a couple different ways:

1. Using the generated Core Data accessor:

    NSSet * apartments = [myLease apartments]; \nNSUInteger numberOfApartments = [apartments count];  

2. Using KeyPaths:

    NSSet * apartments = [myLease valueForKey:@"apartments"]; \nNSUInteger numberOfApartments = [apartments valueForKey:@"@count"];  

3. Using KVC (if your class is fully KVC-compliant):

    NSUInteger numberOfApartments = [myLease countOfApartments];  

4. Using a fetch request:

    NSFetchRequest * r = [[NSFetchRequest alloc] init]; \n[r setEntity:apartmentEntityDescription]; \n[r setPredicate:[NSPredicate predicateWithFormat:@"lease = %@", myLease]]; \nNSArray * apartments = [myManagedObjectContext executeFetchRequest:r error:nil]; \nNSUInteger numberOfApartments = [myManagedObjectContext countForFetchRequest:r error:nil]; \n[r release];  

Feel free to mix-and-match those lines.