Core Data Fetch To Many - iphone

Question

I am trying to fetch all categories, and their sub categories, and display them all in a table. I know how to fetch all categories, but I need to fetch all sub categories, and sort them by category using a fetch results controller. Any ideas of suggestions?

Answer 1

You can create a fetched results controller that fetches SubCategory entities and groups them into sections according to the Category:
// Fetch "SubCategory" entities:
NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:#"SubCategory"];
// First sort descriptor for grouping the cells into sections, sorted by category name:
NSSortDescriptor *sort1 = [NSSortDescriptor sortDescriptorWithKey:#"category.name" ascending:YES];
// Second sort descriptor for sorting the cells within each section:
NSSortDescriptor *sort2 = [NSSortDescriptor sortDescriptorWithKey:#"name" ascending:YES];
request.sortDescriptors = [NSArray arrayWithObjects:sort1, sort2, nil];
self.fetchedResultsController = [[NSFetchedResultsController alloc]
initWithFetchRequest:request
managedObjectContext:context
sectionNameKeyPath:#"category.name"
cacheName:nil];
[self.fetchedResultsController setDelegate:self];
NSError *error;
BOOL success = [self.fetchedResultsController performFetch:&error];
Then you can use the usual table view data source methods as described in the NSFetchedResultsController Class Reference.
This gives you a table view with one table view section for each category.

Answer 2

so, you have the categories in the fetchedResultsController.fetchedObjects
since each subCategory is essentially contained in the Category you can access each by calling [Category valueForKey:#"subCategory"
this will give you an NSSet that you can then sort out (to an NSArray) and use as data for your tableView.
It won't be contained in a fetchedResultsController though.

Answer 3

If you have the option u can do it in other way also if u like.
Take all The Category objects in arrayOfCategories
-(NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection (NSInteger)section:
{
Category *cat = [ arrayOfCategories objectAtIndex:indexPath.row]
if(arrayToHoldObjects.count > 0)
{
[arrayToHoldObjects removeAllObject];
}
for(Subcategory *sub in Category.subcategory)
{
[arrayToHoldObjects addObject:sub];
}
return arrayToHoldObjects.count;
}
- (UITableViewCell *)tableView:(UITableView *)tableView
cellForRowAtIndexPath:(NSIndexPath *)indexPath {
Category *cat = [ arrayOfCategories objectAtIndex:indexPath.row]
if(arrayToHoldObjects.count > 0)
{
[arrayToHoldObjects removeAllObject];
}
for(Subcategory *sub in Category.subcategory)
{
[arrayToHoldObjects addObject:sub];
}
Subcategory *sub = [arrayToHoldObjects objectAtIndexPath.row]
for(int k =0 ; k < arrayToHoldObjects .count; k++)
{
// do what ever u like with sub
return cell;
}
}