Error inserting new relation

[callzhang]

In Basic Example, I added a new Artist object with relation to Song, which also has relation to Genre:

Artist *artist = [NSEntityDescription insertNewObjectForEntityForName:@"Artist" inManagedObjectContext:context];
Song *song = [NSEntityDescription insertNewObjectForEntityForName:@"Song" inManagedObjectContext:context];
Genre *genre = [NSEntityDescription insertNewObjectForEntityForName:@"Genre" inManagedObjectContext:context];
artist.artistName = @"New";
genre.genreName = @"My genre";
song.songTitle = @"Song title";
song.songArtist = artist;
song.songGenre = genre;
NSError *err;
[context save:&err];
if (err) {
    NSLog(@"%@", err.description);
}

But the IncrementalStore threw an error as follows. What's rather interesting is that the code works sometime and doesn't work some other times.
I tried to delete the relation definition on Parse.com and it still works. It seems that the framework doesn't use relation definition on Parse to get the related item.

2014-05-11 02:16:02.878 Basic Example[3147:1303] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: '(null)'
*** First throw call stack:
(
0 CoreFoundation 0x02e1b1e4 __exceptionPreprocess + 180
1 libobjc.A.dylib 0x02b9a8e5 objc_exception_throw + 44
2 Basic Example 0x0013df7b PFSaveManagedObjectContextOrThrowInternalConsistencyException + 331
3 Basic Example 0x0014997c __80-[PFIncrementalStore newValueForRelationship:forObjectWithID:withContext:error:]_block_invoke_5 + 28
4 CoreData 0x00d1984f developerSubmittedBlockToNSManagedObjectContextPerform + 95
5 libdispatch.dylib 0x0312f4d0 _dispatch_client_callout + 14
6 libdispatch.dylib 0x0311c740 _dispatch_barrier_sync_f_invoke + 58
7 libdispatch.dylib 0x0311c3ea dispatch_barrier_sync_f + 89
8 CoreData 0x00d1977f -[NSManagedObjectContext performBlockAndWait:] + 127
9 Basic Example 0x00149924 __80-[PFIncrementalStore newValueForRelationship:forObjectWithID:withContext:error:]_block_invoke_4 + 196
10 CoreData 0x00d1984f developerSubmittedBlockToNSManagedObjectContextPerform + 95
11 CoreData 0x00d1978c -[NSManagedObjectContext performBlockAndWait:] + 140
12 Basic Example 0x0014974e __80-[PFIncrementalStore newValueForRelationship:forObjectWithID:withContext:error:]_block_invoke_3 + 1758
13 Basic Example 0x0014b20c -[PFIncrementalStore insertOrUpdateObjects:ofEntity:withContext:error:completionBlock:] + 460
14 Basic Example 0x00148f4c __80-[PFIncrementalStore newValueForRelationship:forObjectWithID:withContext:error:]_block_invoke_2 + 1180
15 CoreData 0x00d91fe3 developerSubmittedBlockToNSManagedObjectContextPerform_privateasync + 83
16 libdispatch.dylib 0x0312f4d0 _dispatch_client_callout + 14
17 libdispatch.dylib 0x0311d047 _dispatch_queue_drain + 452
18 libdispatch.dylib 0x0311ce42 _dispatch_queue_invoke + 128
19 libdispatch.dylib 0x0311dde2 _dispatch_root_queue_drain + 78
20 libdispatch.dylib 0x0311e127 _dispatch_worker_thread2 + 39
21 libsystem_pthread.dylib 0x0345edab _pthread_wqthread + 336
22 libsystem_pthread.dylib 0x03462cce start_wqthread + 30
)
libc++abi.dylib: terminating with uncaught exception of type NSException

[luke0x]

@callzhang Did you discover a way to fix this? Experiencing the same issue with the Basic Example + MagicalRecord Example apps.

@sbonami Curious if you have any thoughts too...

[callzhang]

@luke0x I pretty much fixed it on my last pull request. Since @sbonami provided me the admin rights, I haven't had a chance to get out of my daily work but I have some plan to do it very soon.

[luke0x]

@callzhang Nice, I'll take a look. Thanks for getting back.