Core Data Migration: How to delete the Core Data stack?

Question

My plan is to delete the old Core Data stack (the NSManagedObjectModel .momd file & the NSPersistentStore .sqlite file) b

Answer 1

It is a perfectly valid thing to do if your app requires internet access anyway. Otherwise users may be left with an empty data set (you delete the old database when you find it's incompatible with the current model, but you cannot re-populate it without access to the server).

Technically, that's a trivial thing to do. When you set up the NSPersistentStoreCoordinator:

NSURL *storeURL = ...;
NSManagedObjectModel *managedObjectModel = ...;
NSError *error = nil;
_persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel: managedObjectModel];

// Check if we already have a persistent store
if ( [[NSFileManager defaultManager] fileExistsAtPath: [storeURL path]] ) {
    NSDictionary *existingPersistentStoreMetadata = [NSPersistentStoreCoordinator metadataForPersistentStoreOfType: NSSQLiteStoreType URL: storeURL error: &error];
    if ( !existingPersistentStoreMetadata ) {
        // Something *really* bad has happened to the persistent store
        [NSException raise: NSInternalInconsistencyException format: @"Failed to read metadata for persistent store %@: %@", storeURL, error];
    }

    if ( ![managedObjectModel isConfiguration: nil compatibleWithStoreMetadata: existingPersistentStoreMetadata] ) {
        if ( ![[NSFileManager defaultManager] removeItemAtURL: storeURL error: &error] )
            NSLog(@"*** Could not delete persistent store, %@", error);
    } // else the existing persistent store is compatible with the current model - nice!
} // else no database file yet

[_persistentStoreCoordinator addPersistentStoreWithType: NSSQLiteStoreType 
                                          configuration: nil 
                                                    URL: storeURL 
                                                options: nil 
                                                  error: &error];