Running Database Fetch (Core Data) in Background Thread using magical Record

  To run database fetching in background thread(in a separate context), so that the UI does not get blocked:

__block NSMutableArray *dataArray= [[NSMutableArray alloc] init];

  // Create a child context of the main context

  NSManagedObjectContext *privateContext = [NSManagedObjectContext MR_context];

  // When using private contexts execute the core data code in it's private queue using performBlock: or performBlockAndWait:

  [privateContext performBlock:^{

    // Execute fetch

  NSArray *privateObjects;

  if(entity_predicate == nil) {

      //fetch all! duh!

      privateObjects = [self MR_findAllSortedBy:sort_key ascending:YES inContext:privateContext];

    } else {

      privateObjects = [self MR_findAllSortedBy:sort_key ascending:YES withPredicate:entity_predicate inContext:privateContext];

    }

   

    // Convert fetched objects into object IDs which can be pulled out of the main context

    NSArray *privateObjectIDs = [privateObjects valueForKey:@"objectID"];

    // Return to main thread

    dispatch_async(dispatch_get_main_queue(), ^{

      // Create a new predicate to pull objects out

      NSArray *finalResults;

      if(privateObjectIDs) {

      NSPredicate *mainPredicate = [NSPredicate predicateWithFormat:@"self IN %@", privateObjectIDs];

      // Execute fetch

        finalResults = [self MR_findAllWithPredicate:mainPredicate];

      }

      // use finalResults from the main thread

      [dataArray removeAllObjects];

      dataArray = [finalResults mutableCopy];

      if (fcb) {

        fcb(dataArray);

      }

     

    });

  }];