Generic way to create cache names for NSFetchedResultsController

Question

I am writing an app with a lot of different NSFetchedResultsController instances which I create in a factory method.

Now I am trying to generically create a cache name for the controller from its attributes (concatenate entity name, predicate, sorting information...).

If anyone has done this before, please share your experience:

• Is it a good approach?
• How exactly should I create the cache name?

As a side thought:

I am also wondering why this isn't already handled by the NSFetchedResultsControllers implementation itself. Why would I ever want to manually assign some cache name, this seems to be an error-prone overhead! Or am I missing something here?

Answer 1

I am astonished, nobody seems to be interested. I would have guessed, everybody who deals with a lot of dynamically created resultsControllers would need this!

Anyway, here is my solution:

// NSFetchedResultsController+GenericCache

- (id)initWithFetchRequest:(NSFetchRequest *)fetchRequest
      managedObjectContext:(NSManagedObjectContext *)context
        sectionNameKeyPath:(NSString *)sectionNameKeyPath
                  useCache:(BOOL)useCache {
    NSString *cacheId = nil;
    if (useCache) {
        cacheId = [NSString stringWithFormat:@"%@-%@-%@"
                   , sectionNameKeyPath
                   , [fetchRequest entityName]
                   , [[fetchRequest predicate] predicateFormat]];
        for (NSSortDescriptor *descriptor in [fetchRequest sortDescriptors]) {
            NSString *sortId = [NSString stringWithFormat:@"-%@-%@-%@"
                                , [descriptor key]
                                , ([descriptor ascending]) ? @"ascending": @"descending"
                                , NSStringFromSelector([descriptor selector])];
            cacheId = [cacheId stringByAppendingString:sortId];
        }
    }
    return [self initWithFetchRequest:fetchRequest
                 managedObjectContext:context
                   sectionNameKeyPath:sectionNameKeyPath
                            cacheName:cacheId];
}

- (void)deleteCache {
    [[self class] deleteCacheWithName:[self cacheName]];
}

I am still testing and I am very open to critique & suggestions for improvement.

Please help making this reliable.