Array Index Out of Bounds issue (NSRangeException) in -[NSManagedObjectContext save:]

Question

My iOS application just crashed with a NSRangeException on -[NSManagedObjectContext save:]. Nothing else helpful anywhere to be found. How am I supposed to fix this? I don't get any memory address or anything that I can work with...

2015-04-22 14:16:38.078 heavenhelp[33559:1734247] *** Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[__NSArrayM objectAtIndex:]: index 6 beyond bounds [0 .. 5]'
*** First throw call stack:
(
    0   CoreFoundation                      0x0167f746 __exceptionPreprocess + 182
    1   libobjc.A.dylib                     0x00f40a97 objc_exception_throw + 44
    2   CoreFoundation                      0x01553b73 -[__NSArrayM objectAtIndex:] + 243
    3   CoreData                            0x00859cf3 -[NSSQLCore recordToManyChangesForObject:inRow:usingTimestamp:inserted:] + 2531
    4   CoreData                            0x00856a0b -[NSSQLCore _populateRow:fromObject:timestamp:inserted:] + 2923
    5   CoreData                            0x00776e24 -[NSSQLCore prepareForSave:] + 1764
    6   CoreData                            0x00775e3d -[NSSQLCore saveChanges:] + 461
    7   CoreData                            0x0073f15e -[NSSQLCore executeRequest:withContext:error:] + 638
    8   CoreData                            0x0083ee75 __65-[NSPersistentStoreCoordinator executeRequest:withContext:error:]_block_invoke + 5349
    9   CoreData                            0x008492ff gutsOfBlockToNSPersistentStoreCoordinatorPerform + 191
    10  libdispatch.dylib                   0x035f4bef _dispatch_client_callout + 14
    11  libdispatch.dylib                   0x035d7b0d _dispatch_barrier_sync_f_invoke + 144
    12  libdispatch.dylib                   0x035d723f dispatch_barrier_sync_f + 105
    13  CoreData                            0x008383f7 _perform + 183
    14  CoreData                            0x0073ec8b -[NSPersistentStoreCoordinator executeRequest:withContext:error:] + 459
    15  CoreData                            0x0076ee09 -[NSManagedObjectContext save:] + 1529
    16  heavenhelp                          0x000b6834 _TF10heavenhelp11saveContextFT_T_ + 324
    17  heavenhelp                          0x0015368d _TFC10heavenhelp26ConversationViewController17viewWillDisappearfS0_FSbT_ + 701
    18  heavenhelp                          0x001536ef _TToFC10heavenhelp26ConversationViewController17viewWillDisappearfS0_FSbT_ + 63
    19  UIKit                               0x020a4292 -[UIViewController _setViewAppearState:isAnimating:] + 706
    20  UIKit                               0x020a4904 -[UIViewController __viewWillDisappear:] + 106
    21  UIKit                               0x020bcd1d -[UIViewController(UIContainerViewControllerProtectedMethods) beginAppearanceTransition:animated:] + 200
    22  UIKit                               0x020cafec -[UINavigationController _startCustomTransition:] + 1028
    23  UIKit                               0x020d8e00 -[UINavigationController _startDeferredTransitionIfNeeded:] + 712
    24  UIKit                               0x020d9a51 -[UINavigationController __viewWillLayoutSubviews] + 57
    25  UIKit                               0x02253750 -[UILayoutContainerView layoutSubviews] + 213
    26  UIKit                               0x01fce57a -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 668
    27  libobjc.A.dylib                     0x00f56771 -[NSObject performSelector:withObject:] + 70
    28  QuartzCore                          0x01d5ee47 -[CALayer layoutSublayers] + 144
    29  QuartzCore                          0x01d52925 _ZN2CA5Layer16layout_if_neededEPNS_11TransactionE + 403
    30  QuartzCore                          0x01d5277a _ZN2CA5Layer28layout_and_display_if_neededEPNS_11TransactionE + 26
    31  QuartzCore                          0x01caec52 _ZN2CA7Context18commit_transactionEPNS_11TransactionE + 284
    32  QuartzCore                          0x01cb00e5 _ZN2CA11Transaction6commitEv + 487
    33  QuartzCore                          0x01cb07fc _ZN2CA11Transaction17observer_callbackEP19__CFRunLoopObservermPv + 92
    34  CoreFoundation                      0x015a086e __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 30
    35  CoreFoundation                      0x015a07b0 __CFRunLoopDoObservers + 400
    36  CoreFoundation                      0x015961ea __CFRunLoopRun + 1226
    37  CoreFoundation                      0x01595a5b CFRunLoopRunSpecific + 443
    38  CoreFoundation                      0x0159588b CFRunLoopRunInMode + 123
    39  GraphicsServices                    0x046cc2c9 GSEventRunModal + 192
    40  GraphicsServices                    0x046cc106 GSEventRun + 104
    41  UIKit                               0x01f3b106 UIApplicationMain + 1526
    42  heavenhelp                          0x000a5c94 main + 180
    43  libdyld.dylib                       0x0361fac9 start + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException

This is the code I used to make my save: thread-safe:

static var onceToken: dispatch_once_t = 0
static var singleton: CoreDataHelper!
static var sharedInstance: CoreDataHelper {
    get {
        dispatch_once(&onceToken, {
            self.singleton = CoreDataHelper()
        })
        return singleton
    }
}

My xcdatamodeld (the relevant part):

Edits: I have edited the code to reflect my changes to make my NSManagedObjectContext thread-safe. Everything I do now, I do on one instance of my CoreDataHelper that I initialise as above. I have found I can trigger a crash by going into one conversation, adding a message, going into another conversation and adding a message there. I have added my xcdatamodeld.

Answer 1

I had apparently set my one-to-many relationship between conversations and messages to "ordered". This was not correct... I had already changed my NSManagedObject's class to use NSMutableSet instead of NSMutableOrderedSet.

Apparently this results in an NSRangeException in the save method...