Zone values for transaction propagation

TransactionManager.dart

import 'dart:async';
import 'dart:math';

import 'package:sembast/sembast.dart';
import 'package:sembast/sembast_io.dart';

Future<void> main() async {
  final dbPath = 'sample-${Random().nextInt(10000)}.db';
  final dbFactory = databaseFactoryIo;
  final db = await dbFactory.openDatabase(dbPath);
  final transactionManager= TransactionManager(db);
  final eventStore = EventStore(db, transactionManager);

  // Successful transaction:
  await transactionManager.transaction(() async {
    await eventStore.put('event1', '{ "id": "event1" }');
  });
  print(await eventStore.get('event1'));

  // Aborted transaction:
  try {
    await transactionManager.transaction(() async {
      await eventStore.put('event2', '{ "id": "event2" }');
      throw AssertionError('no more db for you');
      await eventStore.put('event3', '{ "id": "event3" }');
    });
  } catch (e) {
    print("Expected error occurred");
  }
  print(await eventStore.get('event2')); // => null
}

class EventStore {
  Database db;
  TransactionManager transactionManager;
  StoreRef<String, String> store = StoreRef.main();
  EventStore(this.db, this.transactionManager);
  Future<void> put(String eventId, String json) async {
    final tx = transactionManager.currentTransaction();
    await store.record(eventId).put(tx, json);
  }

  Future<String?> get(String eventId) => store.record(eventId).get(db);
}

class TransactionManager {
  Database db;
  TransactionManager(this.db);

  Future<T> transaction<T>(Future<T> Function() f) async {
    return await db.transaction((tx) async {
      return await runZoned(() async {
        return await f();
      }, zoneValues: {'tx': tx});
    });
  }

  Transaction currentTransaction() => Zone.current['tx'] as Transaction;
}