Realm RxJava write transaction

gistfile1.java

catService.getCats()
          .subscribeOn(Schedulers.io()) 
  .retry()
  .subscribe(catsBO -> {
      try(Realm realm = Realm.getDefaultInstance()) {
        Cat defaultCat = new Cat();
        long rank;
        if(realm.where(Cat.class).count() > 0) {
            rank = realm.where(Cat.class).max(CatFields.RANK).longValue();
        } else {
            rank = 0;
        }
        for(CatBO catBO : catsBO.getCats()) {
            defaultCat.setId(catBO.getId());
            defaultCat.setRank(++rank);
            defaultCat.setUrl(catBO.getUrl());
            realm.insertOrUpdate(defaultCat);
        }
      } // auto-close because of try-with-resources
  }, throwable -> {
    Log.e(TAG, "An error occurred", throwable);
  });