A dead simple JSON based key/value store that is unbelievably useful for scripts and tools

database.dart

import 'dart:convert';
import 'dart:io';

class Database {
  /// A simple JSON file database
  Database(String path) : file = File(path);

  final File file;

  var _store = <String, dynamic>{};

  /// Fetch the file database and hold it in memory.
  Future<void> initState() async {
    try {
      final string = await file.readAsString();
      _store = jsonDecode(string);
    } on FileSystemException catch (e) {
      switch (e.osError.errorCode) {

        /// No such file or directory
        case 2:
          await file.create(recursive: true);
          break;

        default:
          rethrow;
      }
    } on FormatException catch (_) {
      await file.writeAsString('{}');
    }
  }

  /// Read a key from the database
  Future<dynamic> read(String key) async {
    return _store[key];
  }

  /// Set a key in the database. Inserts/updates automatically.
  Future<void> upsert(String key, dynamic value) async {
    _store[key] = value;
    await _updateFileFromStore();
  }

  /// Delete a key in the database.
  Future<void> delete(String key, dynamic value) async {
    _store.remove(key);
    await _updateFileFromStore();
  }

  Future<void> _updateFileFromStore() async {
    final encoder = JsonEncoder.withIndent('  ');
    final prettyprint = encoder.convert(_store);

    await file.writeAsString(prettyprint);
  }
}

example.dart

import 'database.dart';

void main() async {
  /// Setup database
  final db = Database('example_database.json');
  await db.initState();

  /// Add an entry
  await db.upsert('key', 'value');

  /// Returns `value`
  print(await db.read('key'));

  /// Delete the entry
  await db.delete('key', 'value');

  /// Returns `null`
  print(await db.read('key'));

  /// Save an entry for posterity
  await db.upsert('graffiti', 'you wuz here ${DateTime.now().year}');
}

example_database.json

{
  "graffiti": "you wuz here 2021"
}