Hello, I am using an NSFetchedResultsCountroller to execute a query against a Core Data database backed by a sqlite data store. I would like to sort the results by an NSString property of my NSManagedObject. However, if the property is nil or an empty string, I would like those results to appear at the end of my UITableView instead of the beginning. (Think sorting in iTunes by artist. I want the songs with no artist to appear at the end instead of the beginning of my list.)
The first thing I tried to do was to create a category on NSString and create a new comparison method which would sort exactly how I want. This did not work and gave me the following error message: *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'unsupported NSSortDescriptor selector: myComparisonMethod:' I believe this is because the sorting is done by the database and Core Data has a very explicit list of allowed selectors for NSSortDescriptors in my situation. The second solution I considered involved manually sorting the results in-memory. However, that would make me lose out on a lot of NSFetchedResultsController functionality as I would no longer be able to use it for UITableView sections or automatic updating of edited NSManagedObjects. That also seems inefficient as NSFetchedResultsCountroller doesn't necessarily bring all of the results into memory at the same time and only loads objects on an as-needed basis. The final solution I considered involved modifying the data stored in the database such that instead of storing nil or blank for this property, it would instead store something that would most likely sort to the end of the list (like @"zzzzzzzz"). This, however, seems like a big hack and would necessitate changing a lot of my code to account for this. That, and I do not like the idea of messing with the data in my database just to get this sorting problem to work. Finally, I thought about using two NSFetchedResultsController instead of one. One for all entities that have this property set, and one for all that do not. I'd prefer not to do this as it would overly complicate a lot of my code. If I could just get the data to come back sorted correctly, all of my existing code would "just work". However, of all the ideas I've had so far, I think that this one is the best. Am I missing something here? Is there a better way to perform this kind of sort? Does anyone have any recommendations? Maybe there is a way to use two NSSortDescriptors? One that will first sort on the emptiness of the property and a second that will sort on the property itself? Many thanks, Sebastian _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
