Deleting entity in MagicalRecord is not persisting

Question

I am having a strange issue with MagicalRecord. Deletes will not persist. When I delete, NSFetchedResultsControllerDelegate correctly sees that the object has been deleted. However, if I close and reopen the app, the entity reappears.

The code I am using to delete the entity is:

ActivityType *activityType = [_fetchedResultsController objectAtIndexPath:indexPath];
[activityType deleteInContext:[NSManagedObjectContext MR_defaultContext]];
[[NSManagedObjectContext MR_defaultContext] MR_saveToPersistentStoreAndWait];

The code I am using for setting up the NSFetchedResultsController is:

NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription
                               entityForName:@"ActivityType" inManagedObjectContext:[NSManagedObjectContext defaultContext]];
[fetchRequest setEntity:entity];

NSSortDescriptor *sort = [[NSSortDescriptor alloc]
                          initWithKey:@"name" ascending:YES];
[fetchRequest setSortDescriptors:[NSArray arrayWithObject:sort]];

NSFetchedResultsController *theFetchedResultsController =
[[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest
                                    managedObjectContext:[NSManagedObjectContext defaultContext] sectionNameKeyPath:nil
                                               cacheName:@"activityTypes"];
_fetchedResultsController = theFetchedResultsController;
_fetchedResultsController.delegate = self;

Based on other SO posts, I also tried to use [NSManagedObjectContext rootSavingContext] in both the setup and deletion (but to no avail).

Answer 1

I've been through hell and back with core data, and I learned a few things. I'm tired so I'll just write a quick summary.

1. When you delete an entity, core data may reject it due to your deletion rules. The reason why my deletes didn't go through is because it needed to be cascade but it was nullify. I think it has to do with somehow leaving entities abandoned. I don't know why that would be cause to prevent deletion, but that's what fixed it in my case. The way I discovered it was through log, I saw some statement about a referenced dependent entity, and I realized that delete rules will apply.

2. When the log says something about a serious error and a listener, check the FRC code. Since this is the listener, your culprit code will be here somewhere. In my case, I disabled [tableview beginUpdates] and [tableview endupdates]. The FRC actually needs this (I thought it was optional). Otherwise, you get some error about inconsistency and managedobjectcontextlistener and how rows need to be added or deleted etc. etc.

3. when you delete, it may actually get saved into the memory local context, but may not get saved to the persistent store. this means that the FRC delegate code will see the changes, but it may not get saved. also, the memory store may not do the deletion rules checks as it passed mine. but the persistent store will do the checks. gotta look into this more.