Fetch Object with relationship with NSFetchedResultsController - objective-c

Question

Here's my problem:
I've got 2 Entities :
Session (Date date, String name, NSSet behaviours)
Behaviour (String category, String Time, String name, NSManagedobject session).
They are in a one-to-many relationship.
In SessioneViewController, I fetch the Session and the Behaviours:
// This is for the fetch request
#property (nonatomic, ratain) NSArray *sessionArray;
// Here I create the Session Object
Session *newSession = [NSEntityDescription insertNewObjectForEntityForName:#"Session" inManagedObjectContext:self.managedObjectContext];
newSession.name = self.lblName.text;
newSession.date = [NSDate date];
self.managedObjectContext save:nil];
// I add the Session into the Array
self.sessionsArray = [self.sessionsArray arrayByAddingObject:newSession];
// Here I create the Behaviour Object:
Comportamento *newBehaviour = [NSEntityDescription insertNewObjectForEntityForName:#"Behaviour" inManagedObjectContext:self.managedObjectContext];
newBehaviour.name = cell.textLabel.text;
newBehaviour.category = #"Relationship";
newBehaviour.time = _lblTimer.text;
// Here I say which Session is part of the Behaviour
// --- EDIT ---
// Error Code: newBehaviour.session = [self.sessionsArray objectAtIndex:indexPath.row];
newBehaviour.session = [self.sessionsArray lastObject];
Then I have two view controller classes in which I want to display the Sessions and then when a Session is selected I want the related Behaviours.
// In "ArchiveSessionVC.h":
#property (nonatomic, strong) NSFetchedResultsController *frs;
// In "ArchiveSessionVC.m":
- (void) viwDidLoad
{
if(![[self frs] performFetch:&e]) {
NSLog(#"Error %#", e);
abort();
}
-(NSFetchedResultsController *)frs {
if (_frs != nil) {
return _frs;
}
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:#"Session" inManagedObjectContext:self.managedObjectContext];
[fetchRequest setEntity:entity];
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:#"date"
ascending:NO];
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];
[fetchRequest setSortDescriptors:sortDescriptors];
_frs = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:nil cacheName:nil];
return _fetchedResultControllerSessions;
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = #"SessioneCell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];
}
Sessione *sessione = [self.fetchedResultControllerSessions objectAtIndexPath:indexPath];
cell.textLabel.text = sessione.nome;
return cell;
}
Here is where I push the Second view controller for display the Behaviuors:
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
// Push del ViewController dei comportamenti:
ArchiveBehaviuorsVC *aBehavioursVC = [[ArchiveBehaviuorsVC alloc] initWithNibName:#"ArchiveBehaviuorsVC" bundle:nil];
aBehavioursVC.sessioneSelezionata = [self.fetchedResultControllerSessions objectAtIndexPath:indexPath];
[self.navigationController pushViewController:aBehavioursVC animated:YES];
}
My ArchiveBehaviuorsVC is like this:
//"ArchiveBehaviuorsVC.h"
#property (nonatomic, strong) Session *selectedSession;
-(NSFetchedResultsController *)fetchedResultControllerBehaviours
{
if (_fetchedResultControllerBehaviours != nil) {
return _fetchedResultControllerBehaviours;
}
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:#"Behaviour" inManagedObjectContext:self.managedObjectContext];
//NSPredicate *predicate = [NSPredicate predicateWithFormat:#"session == %#",self.sessioneSelezionata];
[fetchRequest setEntity:entity];
[fetchRequest setPredicate:predicate];
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:#"nome"
ascending:NO];
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];
[fetchRequest setSortDescriptors:sortDescriptors];
_fetchedResultControllerBehaviours = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:nil cacheName:nil];
return _fetchedResultControllerBehaviours;
}
This is part of the code but it doesn't work. How do I tell the fetchedResultzController to display only the Behaviours associate with the Session?
-- EDIT ---
I found the problem, it wasn't a NSPredicate error, the problem was in this line of code:
// Error Code: newBehaviour.session = [self.sessionsArray objectAtIndex:indexPath.row];
// Right Code:
newBehaviour.session = [self.sessionsArray lastObject];

Answer 1

The predicate
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"session == %#",self.sessioneSelezionata];
looks ok to me.
Are you sure you are obtaining the wrong behavior? Did you try to enable SQL debugging?
-com.apple.CoreData.SQLDebug X
where X can be 1,2 or 3. The higher the value the more SQL output.
In addition, when you do a save ALWAYS pass in an error reference.
NSError* error = nil;
[context save:&error];
The above snippet returns a bool value so check it. If NO is returned print the error.