Question

In the MagicalRecord github docs it states:

MagicalRecord provides a background saving queue so that saving all
data is performed off the main thread, in the background. This means
that it may be necessary to use MR_saveNestedContexts rather than the
typical MR_save method in order to persist your changes all the way to
your persistent store.

looking at the source, I can’t figure out the difference between these two methods minus the dispatch_async command. I see that they both save all nested contexts up to the root, therefore persisting to the store. But why and in what situation would I use one over the other?

Also, as far as just saving a nested context up one level (without persisting to store) I’m assuming I would still use NSManagedObjectContext’s - (BOOL)save:(NSError **)error method?

Below is the source code of the two methods.

- (void) MR_save {
    [self MR_saveErrorHandler:nil];
}

- (void) MR_saveErrorHandler:(void (^)(NSError *))errorCallback {
    [self performBlockAndWait:^{
        [self MR_saveWithErrorCallback:errorCallback];

        if (self.parentContext) {
            [[self parentContext] performBlockAndWait:^{
                [[self parentContext] MR_saveErrorHandler:errorCallback];
            }];
        }
    }];
}

- (void) MR_saveNestedContexts {
    [self MR_saveNestedContextsErrorHandler:nil];
}

- (void) MR_saveNestedContextsErrorHandler:(void (^)(NSError *))errorCallback {
    [self MR_saveNestedContextsErrorHandler:nil completion:nil];
}

- (void) MR_saveNestedContextsErrorHandler:(void (^)(NSError *))errorCallback completion:(void (^)(void))completion {
    [self performBlock:^{
        [self MR_saveWithErrorCallback:errorCallback];

        if (self.parentContext) {
            [[self parentContext] performBlock:^{
                [[self parentContext] MR_saveNestedContextsErrorHandler:errorCallback completion:completion];
            }];
        } else {
            if (completion) {
                dispatch_async(dispatch_get_main_queue(), ^{
                    completion();
                });
            }
        }
    }];
}

Answer 1

The similarity between ‘MR_save’ and ‘MR_saveNestedContexts’ was changed in version 2.0.8 (I was using 2.0.7).

Here is the commit on github: https://github.com/magicalpanda/MagicalRecord/commit/f7c4350e9daf7d90eec83ba5eafeccfa7af34312

And the discussion: https://github.com/magicalpanda/MagicalRecord/issues/305

So to summarize, in version 2.0.8, ‘MR_save’ now only saves the current context, and ‘MR_saveNestedContexts’ recursively saves up to the topmost context.