Iphone – Core data many-to-many relationship – Predicate question

How is it not working? It helps to describe what results you are seeing.

You are not adding your sort descriptors to your NSFetchRequest, at least in the sample you provided.

Your sort descriptors are ineffective. It appears that Patient is a relationship so sorting against the relationship will not work. You would want to do a sort like the following:

NSSortDescriptor *lastNameDescriptor = [[NSSortDescriptor alloc] initWithKey:@"patient.lastName" ascending:YES];
NSSortDescriptor *firstNameDescriptor = [[NSSortDescriptor alloc] initWithKey:@"patient.firstName" ascending:YES];
NSSortDescriptor *dueDateDescriptor = [[NSSortDescriptor alloc] initWithKey:@"dueDate" ascending:NO];
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects: lastNameDescriptor, firstNameDescriptor, dueDateDescriptor, nil];

[fetchRequest setSortDescriptors:sortDescriptors];

[lastNameDescriptor release], lastNameDescriptor = nil;
[firstNameDescriptor release], firstNameDescriptor = nil;
[dueDateDescriptor release], dueDateDescriptor = nil;

You do not need to cast [fetchedResultsController objectAtIndexPath:indexPath] as it returns id.

What are you getting back from the call to [fetchedResultsController objectAtIndexPath:indexPath]? Put a breakpoint here and check the value and make sure you are getting back a NSManagedObject instead of nil. Putting a breakpoint in that method will also confirm that you are getting called.

Your secondKeypathName will not work as mentioned above. You probably want to set it to @"patient.lastName" so that it will match the initial sort I described above.

Your -tableView: titleForHeaderInSection: should be accessing the cache provided by the NSFetchedResultsController instead of assuming that there is going to be a row in the section:

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

Finally, if you want the section to truly display the "lastname, firstname" format then you will need to create a non-transient derived value property on your Patient entity that is the fullName so that you can create your cache based on it. This derived value would then need to be updated any time that the first name or last name were changed.

You're trying to compare a collection (categories.name) to a scalar value (category.name). You need to either use a collection comparator (CONTAINS), or use a predicate modifier (ANY/ALL/SOME, etc).

Try using:

[NSPredicate predicateWithFormat:@"ANY categories.name =[cd] %@", category.name];

Or:

[NSPredicate predicateWithFormat:@"categories.name CONTAINS[cd] %@", category.name];