- (void)observeNumberOfUnreadMessages
{
  LYRQuery *query = [LYRQuery queryWithQueryableClass:[LYRMessage class]];
  query.predicate = [LYRPredicate predicateWithProperty:@"isUnread" predicateOperator:LYRPredicateOperatorIsEqualTo value:@(YES)];
  LYRQueryController *controller = [self.layerManager.layerClient queryControllerWithQuery:query];
  controller.delegate = self;
  self.unreadMessagesQueryController = controller;
}

#pragma mark - LYRQueryController Delegate

- (void)queryControllerDidChangeContent:(LYRQueryController *)queryController
{
  NSInteger numberOfUnreadMessages = queryController.count;
}