Core Data Fetch Async

NSManagedObject+ManagedObject.m

@implementation NSManagedObject (ManagedObject)

+ (void)fetchAsyncToMainContextWithRequest:(void (^)(NSFetchRequest *request))block
                                completion:(void (^)(NSArray *objects))completion
{
	if (!completion) {
		return;
    }
	
	NSManagedObjectContext *mainContext	= [NSManagedObjectContext mainContext];
	NSManagedObjectContext *backgroundContext = [NSManagedObjectContext backgroundContext];
    
	[backgroundContext performBlock:^{
		NSFetchRequest *backgroundRequest = [NSFetchRequest fetchRequestWithEntity:[self class] context:backgroundContext];
		
		if (block) {
			block(backgroundRequest);
        }
		
		[backgroundRequest setResultType:NSManagedObjectIDResultType];
		
		NSError *error = nil;
		NSArray *backgroundObjects = [backgroundContext executeFetchRequest:backgroundRequest error:&error];
        
		if (!error) {
            [mainContext performBlock:^{
                NSMutableArray *objects = [NSMutableArray array];
                [backgroundObjects enumerateObjectsUsingBlock:^(NSManagedObjectID *objId, NSUInteger idx, BOOL *stop) {
                    [objects addObject:[mainContext objectWithID:objId]];
                }];
                
                completion([objects copy]);
            }];
        }
	}];
}

@end