Question

I have this working code, but now i need to be able to change the NSPredicate, based on the object used in the predicateWithFormat as follows:

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

[fetchRequest setPredicate:[NSPredicate predicateWithFormat:@"self.atrObj == %@", _currentUser.atrObj.objectID]];

[fetchRequest setEntity:entity];

NSSortDescriptor *sortContent = [[NSSortDescriptor alloc] initWithKey:@"date" ascending:NO];
[fetchRequest setSortDescriptors:[NSArray arrayWithObject:sortContent]];
[fetchRequest setFetchBatchSize:10];
NSFetchedResultsController *theFetchedResultsController = 
[[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest 
                                    managedObjectContext:_context sectionNameKeyPath:nil 
                                               cacheName:nil];

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

I need the fetchedResultsControlelr to use the new _currentUser object when i change the _currentUser object from the app delegate which has this tableviewcontroller a property.

[self.tableViewcontroller setCurrentUser:user]; 

Thank you!

Answer 1

You can change the predicate anytime but be sure to re-fetch via performFetch. Also from Apple docs:

Important: Important If you are using a cache, you must call deleteCacheWithName: before changing any of the fetch request, its
predicate, or its sort descriptors. You must not reuse the same
fetched results controller for multiple queries unless you set the
cacheName to nil.

Also, from the Apple docs of NSFetchedResultsController:

Modifying the Fetch Request You cannot simply change the fetch request
to modify the results. If you want to change the fetch request, you
must:

• If you are using a cache, delete it (using deleteCacheWithName:).
  Typically you should not use a cache if you are changing the fetch
  request.

• Change the fetch request.

• Invoke performFetch:.