在 sembast 中首次创建时初始化存储

Question

我正在 Flutter 中开发一个移动应用程序，我想管理我的应用程序的设置(浅色主题或深色主题，...

我正在使用sembast来存储应用程序的设置。我想在第一次创建时使用一些初始值初始化存储。我该怎么做？

这是我的数据库帮助程序类：

class AppDatabase {
// Name of the database.
static final String _dbName = 'mydb.db';
// Singleton instance.
static final AppDatabase _singleton = AppDatabase._();
// Singleton getter.
static AppDatabase get instance => _singleton;
// Transforms synchronous code into asynchronous code.
Completer<Database> _dbOpenCompleter;
// Private constructor.
AppDatabase._();
// Database object getter.
Future<Database> get database async {
// If completer is null, AppDatabaseClass is newly instantiated, so database is not yet opened.
if (_dbOpenCompleter == null) {
_dbOpenCompleter = Completer();
_openDatabase();
}
return _dbOpenCompleter.future;
}
Future<void> _openDatabase() async {
// Get a platform-specific directory where persistent app data can be stored.
final appDocumentDir = await getApplicationDocumentsDirectory();
// Path with the form: /platform-specific-directory/demo.db
final dbPath = join(appDocumentDir.path, _dbName);
final database = await databaseFactoryIo.openDatabase(dbPath);
// Any code awaiting the Completer's future will now start executing.
_dbOpenCompleter.complete(database);
}
}

然后，我使用以下存储库对我的设置执行 CRUD 操作：

class SettingsDatabaseRepository implements SettingsRepository {
// The name of the store.
static const String SETTINGS_STORE_NAME = 'settings';
// This store acts like a persistent map, values of which are Settings objects
// converted to Map.
final _settingsStore = intMapStoreFactory.store(SETTINGS_STORE_NAME);
// Private getter to shorten the amount of code needed to get the singleton
// instance of an opened database.
Future<Database> get _db async => await AppDatabase.instance.database;
@override
Future<void> insert(Settings settings) async {
await _settingsStore.add(await _db, settings.toMap());
}
@override
Future<void> update(Settings settings) async {
final finder = Finder(filter: Filter.byKey(settings.settingsId));
await _settingsStore.update(
await _db,
settings.toMap(),
finder: finder,
);
}
@override
Future<Settings> getSettings() async {
final recordSnapshots = await _settingsStore.find(await _db);
final settingsList = recordSnapshots.map((snapshot) {
final settings = Settings.fromMap(snapshot.value);
settings.copyWith(settingsId: snapshot.key);
return settings;
}).toList();
if (settingsList.isEmpty)
return null;
else
return settingsList.first;
}
}

Answer 1

我想

在第一次创建时使用一些初始值初始化存储。

创建存储时无法执行操作(因为存储不是真正创建的，它只保存记录(，但是可以在创建数据库时执行操作。

Sembast支持类似于sqlite的数据库版本控制系统，尽管这里没有太多的模式可以修改。您可以使用此系统在创建数据库时(或稍后在新版本中决定更新数据库时(执行操作。

// Our shop store sample data
var store = intMapStoreFactory.store('shop');
var db = await factory.openDatabase(path, version: 1,
onVersionChanged: (db, oldVersion, newVersion) async {
// If the db does not exist, create some data
if (oldVersion == 0) {
await store.add(db, {'name': 'Lamp', 'price': 10});
await store.add(db, {'name': 'Chair', 'price': 15});
}
});

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