hpoul/simple_json_persistence

simple_json_persistence

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Flutter data storage based on simple json files. The main advantage to using for example the shared preference plugin is that:

1. It is completely written in dart, so no communication with native ios/android code.
2. It is possible to have multiple storages for different base types. While the shared preferences load the whole data into memory at once, this allows you to split it up into multiple json storage. (e.g. one small storage for app data/config which needs to be loaded on startup and a larger json storage with larger application data).

It is still not suitable for large datasets, since all data will be kept in memory and written into the json file at once, but it's a good middle ground between shared preferences and complicated database.

Getting Started

To make use of SimpleJsonPersistence you have to create your data models to serialize to and from json. I personally prefer to use built_value with it's serialization, or json_serializable.

Anyway, it is recommended that persistence models are immutable.

import 'package:simple_json_persistence/simple_json_persistence.dart';

@JsonSerializable(nullable: false)
class MyModel {
  MyModel({this.property,});

  factory MyModel.fromJson(Map<String, dynamic> json) =>
      _$MyModelFromJson(json);

  Map<String, dynamic> toJson() => _$MyModelToJson(this);

  final String property;
}

void doSomething() async {
  final store = SimpleJsonPersistence.forType(
    (json) => MyModel.fromJson(json),
    name = 'MyModel',
  );
  await store.save(MyModel(property: 'foo'));
  final foo = await store.load();

  // since every SimpleJsonPersistence for the same type/name is the same instance
  // you can also subscribe to changes.
  store.onValueChanged.listen((newValue) {
    print('got a new value $newValue');
  });
}

Usage in flutter (StreamBuilder)

See also the example application.

Widget build(BuildContext context) {
  final store = SimpleJsonPersistence.forType(
      (json) => AppData.fromJson(json),
      defaultCreator: () => AppData(counter: 0));
  return StreamBuilder<AppData>(
    stream: store.onValueChangedAndLoad,
    initialData: store.cachedValue,
    builder: (context, snapshot) => Text('Counter: ${snapshot.data?.counter ?? 'Loading'}'),
  );
}