Open Radar

 
Summary:
When using a FRC with a section key path, the results when fetching against a child context are sometimes surprising

Steps to Reproduce:
App Delegate's child managed object context save operation causes managed objects to be saved into it's parent managed object context (colloquially referred to as "pushing saves up one level"). However, if the parent managed object context does not persist these objects to disk (meaning: parentContext.hasChanges == YES), thereby obtaining permanent object IDs, then the fetched results controller does not create sections based on the keypath passed at initialization.

 I believe this has *something* to do with Key-Value Coding. Overriding -[NSManagedObject valueForKeyPath:] yields the following interesting backtrace when the fetched results controller fetches on a dirty managed object context that is directly connected to a persistent store coordinator:

 frame #0:  FetchedResultsController`-[FHKEvent valueForKeyPath:](self=0x08c7dd90, _cmd=0x012a5b93, keyPath=0x00005888) + 57 at FHKEvent.m:15
 frame #1:  CoreData`-[NSFetchedResultsController(PrivateMethods) _sectionNameForObject:] + 50
 frame #2:  CoreData`-[NSFetchedResultsController(PrivateMethods) _computeSectionInfo:error:] + 1151
 frame #3:  CoreData`-[NSFetchedResultsController performFetch:] + 1021
 frame #4:  FetchedResultsController`-[FHKViewController fetchedResultsController](self=0x08a9ef70, _cmd=0x000043e8) + 700 at FHKViewController.m:39
 frame #5:  FetchedResultsController`-[FHKViewController numberOfSectionsInTableView:](self=0x08a9ef70, _cmd=0x00998b00, tableView=0x09295000) + 78 at FHKViewController.m:78
 frame #6:  UIKit`-[UITableViewRowData(UITableViewRowDataPrivate) _updateNumSections] + 102
 frame #7:  UIKit`-[UITableViewRowData invalidateAllSections] + 69
 frame #8:  UIKit`-[UITableView _updateRowData] + 194
 frame #9:  UIKit`-[UITableView _ensureRowDataIsLoaded] + 45
 frame #10:  UIKit`-[UITableView numberOfSections] + 35
 frame #11:  UIKit`-[UITableViewController viewWillAppear:] + 103
 --snip--

However, when the fetched results controller fetches on a "clean" child  (hasChanges == NO) of a dirty parent context (that parent context dirtied  by a save pushing changes up), -[NSManagedObject valueForKeyPath:] isn't called after -[NSFetchedResultsController _computeSectionInfo:error:]. -[NSFetchedResultsController _sectionNameForObject:] isn't called at all in this situation.

Project:
https://github.com/evandelaney/AppleBug-15612154