Question

I have an entity “A” that contains many entity “B”:

I want to retrieve the list of item “B”:

A contains a NSSet of B called “b_list”

NSEntityDescription *selectEntityDescription = [NSEntityDescription
                                                    entityForName:@"A" inManagedObjectContext:self.managedObjectContext];
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    [fetchRequest setEntity:selectEntityDescription];
    [fetchRequest setRelationshipKeyPathsForPrefetching:[NSArray arrayWithObject:@"B"]];
    [fetchRequest setReturnsObjectsAsFaults:NO];

    NSPredicate *whereForFetch = [NSPredicate predicateWithFormat:@"id == %@", object_id];
    [fetchRequest setPredicate:whereForFetch];

    NSError *error = nil;
    NSArray *array = [managedObjectContext executeFetchRequest:fetchRequest error:&error];
    A *a = nil;
    if (array != nil && [array count] > 0){
        NSLog(@"A exist"); //return "A exist"
        a = [array objectAtIndex:0];
        NSLog(@"a b_list %@",a.b_list); //return a Fault result
        NSLog(@"a b_list count %d",a.b_list.count); //return 0
        for (B *b in a.b_list){ //not executed
            NSLog(@"b %@",b.name);
        }
    }

I don’t understand why it still return a fault result and not the list of objects.

Answer 1

It will return a fault if B is empty. Since your not seeing the code inside of your for loop then it is a strong bet that it is empty.