Core Data Transaction-like Method

gistfile1.m

- (BOOL)performBlockAndSaveOrReset:(BOOL (^)(NSError *__autoreleasing *))block error:(NSError *__autoreleasing *)error
{
    __block BOOL blockOk, saveOk;
    __block NSError *blockError, saveError;
    [self performBlockAndWait:^{
        blockOk = block(&blockError);
        if (! blockOk) {
            [self reset]; return;
        }

        if (! [self hasChanges]) {
            saveOk = YES; return;
        }

        saveOk = [self save:&saveError];
        if (! saveOk) {
            [self reset]; return;
        }
    }];

    if (error) {
        *error = blockError ?: saveError;
    }

    return blockOk && saveOk;
}