Reputation: 5817
I have two tables with the following structure
MainCategory:
name position hasSubCategories
SubCategory:
name position display belongsToMainCategory
Now I want to display all subcategories (where display attribute = YES) grouped by main category. The main category sections should be sorted as defined by position and the subcategories itself (within the section) by their position attribute. (name by the way can be the same for a certain main category...my tables have more attributes but they aren't relevant to understand the problem). But my order is completely messed up. Why? Here's my code for the FetchedResultsController:
NSError *error = nil;
NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"SubCategory"];
NSSortDescriptor *mainCatPosition = [[NSSortDescriptor alloc]
initWithKey:@"belongsToMainCategory.position" ascending:YES];
NSSortDescriptor *subCatPosition = [[NSSortDescriptor alloc]
initWithKey:@"position" ascending:YES];
request.sortDescriptors = [NSArray arrayWithObjects:mainCatPosition,subCatPosition,nil];
request.predicate = [NSPredicate predicateWithFormat:@"display = %@", [NSNumber numberWithBool:YES]];
[self.db.managedObjectContext executeFetchRequest:request error:&error];
self.fetchedResultsController = [[NSFetchedResultsController alloc]initWithFetchRequest:request
managedObjectContext:self.budgetDatabase.managedObjectContext
sectionNameKeyPath:@"belongsToMainCategory.name"
cacheName:nil];
Upvotes: 1
Views: 510
Reputation: 540105
The key path used as sectionNameKeyPath:
argument to the fetched results controller must
be the same key that is used in the first sort descriptor or generate the same relative ordering.
The fetched results controller first orders all fetched objects according to the first
sort descriptor and then groups the objects into sections according to the sectionNameKeyPath
. Therefore using different key paths (as in your case "belongsToMainCategory.position" vs. "belongsToMainCategory.name") does not work.
This could even cause a runtime error about "out of order sections".
Upvotes: 6