Core Data NSSet Issue

Question

I auto-generated the cored data NSManagedObject class, and what I am trying to do is to display all phone numbers for a certain person. I am trying to display this in my table view class to populate the table.

Person to Numbers is a one-to-many relationship, and the numbers are in the set which I did by the addNumbersObject method. I just do not understand how to fetch this in the fetchresultscontroller and display them in the table view.

Currently I am just fetching all people.

Any ideas or suggestions?

Core Data Class:

@class Number

@interface Person : NSManagedObject

@property (nonatomic, retain) NSString *name;
@property (nonatomic, retain) NSSet *numbers;

@end

@interface Person (CoreDataGeneratedAccessors)

- (void)addNumbersObject:(Number *)value;
- (void)removeNumbersObject:(Number *)value;
- (void)addNumbers:(NSSet *)values;
- (void)removeNumbers:(NSSet *)values;

@end

Table View Class:

- (NSFetchedResultsController *)fetchedResultsController 
{    
    if (_fetchedResultsController != nil)
        return _fetchedResultsController;

    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Person" inManagedObjectContext:_context];
    [fetchRequest setEntity:entity];

    NSSortDescriptor *sort = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:NO];
    [fetchRequest setSortDescriptors:[NSArray arrayWithObject:sort]];
    [fetchRequest setFetchBatchSize:20];

    NSFetchedResultsController *theFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:_context sectionNameKeyPath:nil cacheName:@"Root"];

    self.fetchedResultsController = theFetchedResultsController;
    _fetchedResultsController.delegate = self;

    [fetchRequest release];
    [theFetchedResultsController release];

    return _fetchedResultsController;      
}

Answer 1

Try using a predicate on your fetchRequest.

I am not sure from your question if you want to display all the phone numbers for all the people or how you want that formatted, but this is how to get all the numbers for one person.

To get all the phone numbers for one specific person in one table view:

NSEntityDescription *entity = [NSEntityDescription entityForName:@"Number" inManagedObjectContext:_context];

[fetchRequest setPredicate:[NSPredicate predicateWithFormat:@"person.name == %@", personName]]; //Assuming person.name is unique

Then sort that person's phone number like you want it.

Answer 2

There are a lot of ways you might "display all phone numbers for a person" -- think specifically about what you want your table to contain and how it should be organized, and you might have an easier time finding the answer you're looking for.

In the meantime, here's one approach: Use table sections to represent Persons, and rows within each for their associated Numbers. You can do this like so:

1. Set Number as the entity for your fetch request.
2. Set "person.name" as the sort key. (You might want to add a second sort descriptor so that Numbers for each person are in a sensible order.)
3. Also set "person.name" as the section name key path.

4. Implement your table view data source's -tableView:titleForHeaderInSection: thusly:

   - (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section { 
       id <NSFetchedResultsSectionInfo> sectionInfo = [[self.fetchedResultsController sections] objectAtIndex:section];
       return [sectionInfo name];
   }