IsolatedHive allows you to safely use Hive in a multi-isolate environment by maintaining its own separate isolate for Hive operations

Here are some common examples of multi-isolate scenarios:

• A Flutter desktop app with multiple windows
• Running background tasks with flutter_workmanager, background_fetch, etc
• Push notification processing

IsolatedHive has a very similar API to Hive, but there are some key differences:

• The init call takes an isolateNameServer parameter
• Most methods are asynchronous due to isolate communication
• IsolatedHive does not support HiveObject or HiveList
• Isolate communication does add some overhead. See the benchmarks above.

NOTE: On web, IsolatedHive directly calls Hive since web does not support isolates

Usage

import 'package:hive_ce/hive.dart';

import 'stub_ins.dart';

void main() async {
  await IsolatedHive.init('.', isolateNameServer: StubIns());
  final box = await IsolatedHive.openBox('box');
  await box.put('key', 'value');
  print(await box.get('key')); // reading is async
}

NOTE: It is possible to use IsolatedHive without an IsolateNameServer, BUT THIS IS UNSAFE. The IsolateNameServer is what allows IsolatedHive to locate and communicate with a single backend isolate.

Additional notes:

• With Flutter, use IsolatedHive.initFlutter from hive_ce_flutter to initialize IsolatedHive with Flutter's IsolateNameServer
• There is also an IsolatedHive.registerAdapters method if you use hive_ce_generator to generate adapters

Example

See an example of a multi-window Flutter app using IsolatedHive here

Hive not only supports primitives, lists, and maps but also any Dart object you like. You need to generate type adapters before you can store custom objects.

Create model classes

import 'package:hive_ce/hive.dart';

class Person extends HiveObject {
  Person({required this.name, required this.age});

  String name;
  int age;
}

Create a GenerateAdapters annotation

Usually this is placed in lib/hive/hive_adapters.dart

import 'package:hive_ce/hive.dart';
import 'person.dart';

@GenerateAdapters([AdapterSpec<Person>()])
part 'hive_adapters.g.dart';

Update pubspec.yaml

dev_dependencies:
  build_runner: latest
  hive_ce_generator: latest

Run build_runner

dart pub run build_runner build --delete-conflicting-outputs

This will generate the following:

• TypeAdapters for the specified AdapterSpecs
• TypeAdapters for all explicitly defined HiveTypes
• A hive_adapters.g.dart file containing all adapters generated from the GenerateAdapters annotation
• A hive_adapters.g.yaml file
• A hive_registrar.g.dart file containing an extension method to register all generated adapters

All of the generated files should be checked into version control. These files are explained in more detail below.

Use the Hive registrar

The Hive Registrar allows you to register all generated TypeAdapters in one call

import 'dart:io';
import 'package:hive_ce/hive.dart';
import 'package:your_package/hive/hive_registrar.g.dart';

void main() {
  Hive
    ..init(Directory.current.path)
    ..registerAdapters();
}

Using HiveObject methods

Extending HiveObject is optional but it provides handy methods like save() and delete().

import 'package:hive_ce/hive.dart';
import 'person.dart';

void example() async {
  final box = await Hive.openBox('myBox');

  final person = Person(name: 'Dave', age: 22);
  await box.add(person);

  print(box.getAt(0)); // Dave - 22

  person.age = 30;
  await person.save();

  print(box.getAt(0)); // Dave - 30
}

About hive_adapters.g.yaml

The Hive schema is a generated yaml file that contains the information necessary to incrementally update the generated TypeAdapters as your model classes evolve.

Some migrations may require manual modifications to the Hive schema file. One example is class/field renaming. Without manual intervention, the generator will see both an added and removed class/field. To resolve this, manually rename the class/field in the schema.

Explicitly defining HiveTypes

The old method of defining HiveTypes is still supported, but should be unnecessary now that Hive CE supports constructor parameter defaults. If you have a use-case that GenerateAdapters does not support, please create an issue on GitHub.

Unfortunately it is not possible for GenerateAdapters to handle private fields. You can use @protected instead if necessary.

BoxCollections are a set of boxes which can be similarly used as normal boxes, except of that they dramatically improve speed on web. They support opening and closing all boxes of a collection at once and more efficiently store data in indexed DB on web.

Aside, they also expose Transactions which can be used to speed up tremendous numbers of database transactions on web.

On dart:io platforms, there is no performance gain by BoxCollections or Transactions. Only BoxCollections might be useful for some box hierarchy and development experience.

import 'package:hive_ce/hive.dart';
import 'hive_cipher_impl.dart';

void example() async {
  // Create a box collection
  final collection = await BoxCollection.open(
    // Name of your database
    'MyFirstFluffyBox',
    // Names of your boxes
    {'cats', 'dogs'},
    // Path where to store your boxes (Only used in Flutter / Dart IO)
    path: './',
    // Key to encrypt your boxes (Only used in Flutter / Dart IO)
    key: HiveCipherImpl(),
  );

  // Open your boxes. Optional: Give it a type.
  final catsBox = await collection.openBox<Map>('cats');

  // Put something in
  await catsBox.put('fluffy', {'name': 'Fluffy', 'age': 4});
  await catsBox.put('loki', {'name': 'Loki', 'age': 2});

  // Get values of type (immutable) Map?
  final loki = await catsBox.get('loki');
  print('Loki is ${loki?['age']} years old.');

  // Returns a List of values
  final cats = await catsBox.getAll(['loki', 'fluffy']);
  print(cats);

  // Returns a List<String> of all keys
  final allCatKeys = await catsBox.getAllKeys();
  print(allCatKeys);

  // Returns a Map<String, Map> with all keys and entries
  final catMap = await catsBox.getAllValues();
  print(catMap);

  // delete one or more entries
  await catsBox.delete('loki');
  await catsBox.deleteAll(['loki', 'fluffy']);

  // ...or clear the whole box at once
  await catsBox.clear();

  // Speed up write actions with transactions
  await collection.transaction(
    () async {
      await catsBox.put('fluffy', {'name': 'Fluffy', 'age': 4});
      await catsBox.put('loki', {'name': 'Loki', 'age': 2});
      // ...
    },
    boxNames: ['cats'], // By default all boxes become blocked.
    readOnly: false,
  );
}

Hive was written with Flutter in mind. It is a perfect fit if you need a lightweight datastore for your app. After adding the required dependencies and initializing Hive, you can use Hive in your project:

import 'package:hive_ce/hive.dart';
import 'package:hive_ce_flutter/hive_flutter.dart';

class SettingsPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return ValueListenableBuilder(
      valueListenable: Hive.box('settings').listenable(),
      builder: (context, box, widget) {
        return Switch(
          value: box.get('darkMode'),
          onChanged: (val) {
            box.put('darkMode', val);
          }
        );
      },
    );
  }
}

Boxes are cached and therefore fast enough to be used directly in the build() method of Flutter widgets.