NSFetchedResultsController with sections created by first letter of a string

core-data, ios, iphone, objective-c

Solution

I think I've got yet another option, this one uses a category on NSString...

@implementation NSString (FetchedGroupByString)
- (NSString *)stringGroupByFirstInitial {
    if (!self.length || self.length == 1)
        return self;
    return [self substringToIndex:1];
}
@end

Now a little bit later on, while constructing your FRC:

- (NSFetchedResultsController *)newFRC {
    NSFetchedResultsController *frc = [[NSFetchedResultsController alloc] initWithFetchRequest:awesomeRequest
            managedObjectContext:coolManagedObjectContext
            sectionNameKeyPath:@"lastName.stringGroupByFirstInitial"
            cacheName:@"CoolCat"];
    return frc;
}

This is now my favorite approach. Much cleaner/easier to implement. Moreover, you don't have to make any changes to your object model class to support it. This means that it'll work on any object model, provided the section name points to a property based on NSString

Problem

Learning Core Data on the iPhone. There seem to be few examples on Core Data populating a table view with sections. The CoreDataBooks example uses sections, but they're generated from full strings within the model. I want to organize the Core Data table into sections by the first letter of a last name, a la the Address Book. I could go in and create another attribute, i.e. a single letter, for each person in order to act as the section division, but this seems kludgy. Here's what I'm starting with ... the trick seems to be fooling the `sectionNameKeyPath`: ``` - (NSFetchedResultsController *)fetchedResultsController { //.........SOME STUFF DELETED // Edit the sort key as appropriate. NSSortDescriptor *orderDescriptor = [[NSSortDescriptor alloc] initWithKey:@"personName" ascending:YES]; NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:orderDescriptor, nil]; [fetchRequest setSortDescriptors:sortDescriptors]; // Edit the section name key path and cache name if appropriate. // nil for section name key path means "no sections". NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:managedObjectContext sectionNameKeyPath:@"personName" cacheName:@"Root"]; //.... } ```

Original source