ObjectBox for Dart not lazy-loading ToMany relations separately

In the documentation for ObjectBox, they say to-many relations are resolved lazily on first access, and then cached in the source entity inside the ToMany object.

In my app, I want to use a ToMany relationship where one entity A will be linked with a very large number (potentially in the range of thousands) of another entity B. I don't want to load all B at once, because that might slow down the app.

To simulate this, I created a small "banking" Flutter application, with 2 entities Account and Transaction. Here, one account may have a relationship with thousands of transactions.

main.dart is where I initialize ObjectBox. I'm enabling some debug flags because I want to see in the logs when read operations are performed:

// main.dart
void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  final store = Store(
    getObjectBoxModel(),
    directory: 'memory:obx',
    debugFlags: DebugFlags.logTransactionsRead,
  );
  runApp(MainApp(store: store));
}

My entities Account and Transaction are very simple, with only the ID and the relationship.

@Entity()
class Account {
  @Id()
  int id;

  @Backlink('account')
  final transactions = ToMany<Transaction>();

  Account({this.id = 0});
}

@Entity()
class Transaction {
  @Id()
  int id;

  final account = ToOne<Account>();

  Transaction({this.id = 0});
}

Finally, my App. It consists of a column of 3 buttons, one for clearing the database, one for creating data, one one for reading them.

// App.dart
class MainApp extends StatelessWidget {
  final Store store;
  const MainApp({required this.store, super.key});

  Box<Account> get accountBox => store.box<Account>();
  Box<Transaction> get transactionBox => store.box<Transaction>();

  _clear() {
    accountBox.removeAll();
    transactionBox.removeAll();
    print('Cleared all data');
  }

  _create() {
    final account = Account();
    account.transactions.add(Transaction());
    account.transactions.add(Transaction());
    account.transactions.add(Transaction());

    accountBox.put(account);
  }

  _readAccounts() async {
    final accounts = accountBox.getAll();

    for (var account in accounts) {
      print('Account ID: ${account.id}');

      await Future.delayed(const Duration(seconds: 1));
      for (var transaction in account.transactions) {
        print('Transaction ID: ${transaction.id}');
        await Future.delayed(const Duration(seconds: 1));
      }
    }
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            crossAxisAlignment: CrossAxisAlignment.center,
            children: [
              ElevatedButton(onPressed: _clear, child: Text('Clear')),
              SizedBox(height: 20),
              ElevatedButton(onPressed: _create, child: Text('Create')),
              SizedBox(height: 20),
              ElevatedButton(
                onPressed: _readAccounts,
                child: Text('Read Accounts'),
              ),
            ],
          ),
        ),
      ),
    );
  }
}

The _create() function creates 1 account and 3 transactions.

When I execute _readAccounts(), I'm expecting an initial read operation on the Account entity, followed by 3 additional read operation on Transaction every 1 second. In practice, this is not what happens. Here are my logs:

1.  I/Box     (10542): TX #27 (read)
2.  I/Box     (10542): TX #27 to be destroyed on owner thread (last committed: TX #25)...
3.  I/Box     (10542): TX #27 destroyed
4.  I/Box     (10542): TX #28 (read)
5.  I/Box     (10542): TX #28 to be destroyed on owner thread (last committed: TX #25)...
6.  I/Box     (10542): TX #28 destroyed
7.  I/flutter (10542): Account ID: 1
8.  I/Box     (10542): TX #29 (read)
9.  I/Box     (10542): TX #29 to be destroyed on owner thread (last committed: TX #25)...
10. I/Box     (10542): TX #29 destroyed
11. I/Box     (10542): TX #30 (read)
12. I/Box     (10542): TX #30 to be destroyed on owner thread (last committed: TX #25)...
13. I/Box     (10542): TX #30 destroyed
14. I/flutter (10542): Transaction ID: 1
15. I/flutter (10542): Transaction ID: 2
16. I/flutter (10542): Transaction ID: 3

What happens:

• Transactions 27 & 28 (lines 1-6) correspond to the accountBox.getAll() operation. I'm not sure why it needs 2 transactions to do that.
• Then, as soon as I enter the second for loop for (var transaction in account.transactions) { ... }, transactions 29 & 30 (lines 8-13) are executed.
• Finally, lines 14-16 are printed one by one at a 1 second interval.

So yes, the relations are resolved lazily, because objectbox does not read anything until I access account.transactions. But when I do, it loads all relations at once.

Is there any way to resolve them one by one, when/if I need them?