NSFetchedResultsController from multiple entities and updating model - ios

Question

I have existing core data model that has Entity Video.
I want to update an app and I would like to add another entity to the object called Project.
It seems that I achieved this using core data light migration.
Now I would like to Video to be child of the Project. And finally in the UITableView I would like to display Projects as Section headers and Videos as rows.
What would be the best way to accomplish it?
Currently I am using NSFetchedResultsController to query the core data.
thank you

Answer 1

If I'm not mistaken, you can achieve this kind of change using the lightweight migration. You have to create a one-to-many ordered relationship between the Project entity and the Video entity. You can still use NSFetchedResultsController to fetch a list of projects and then traverse the relationship with the Video entity to get the associated objects. It would look more or less like this:
NSEntityDescription *entity = [NSEntityDescription entityForName:#"Project" inManagedObjectContext: context];
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
[fetchRequest setEntity:entity];
[fetchRequest setRelationshipKeyPathsForPrefetching: #"videos"];
NSFetchedResultsController *controller = [[NSFetchedResultsController alloc]
initWithFetchRequest: fetchRequest
managedObjectContext: context
sectionNameKeyPath: nil
cacheName: nil];
We're setting up an NSFetchRequest object to prefetch the "videos" relationship which will save us some time when accessing Video entities. Then, after retrieving a list of Project entities, you would access them in tableView:cellForRowAtIndexPath:
- (NSInteger) numberOfSectionsInTableView: (UITableView*) tableView
{
return [self.fetchedResultsController.fetchedObjects count];
}
- (NSInteger) tableView: (UITablView*) tableView numberOfRowsInSection: (NSInteger) section
{
Project *project = [self.fetchedResultsController.fetchedObjects objectAtIndex: section];
return [project.videos count];
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
...
Project *project = [self.fetchedResultsController.fetchedObjects objectAtIndex: indexPath.section];
Video *video = [project.videos objectAtIndex: indexPath.row];
...
}