Automatically migrate from local storage to IndexedDb

docs/content/en/docs/Other engines/web.md

@@ -80,3 +80,17 @@ object via `window.db`. If you need to quickly run a query to check the state of
 If you need to delete your databases, there stored using local storage. You can clear all your data with `localStorage.clear()`.
 
 Web support is experimental at the moment, so please [report all issues](https://github.com/simolus3/moor/issues/new) you find.
+
+## Using IndexedDb
+
+The default `WebDatabase` uses local storage to store the raw sqlite database file. On browsers that support it, you can also
+use `IndexedDb` to store that blob. In general, browsers allow a larger size for `IndexedDb`. The implementation is also more
+performant, since we don't have to encode binary blobs as strings.
+
+To use this implementation on browsers that support it, replace `WebDatabase(name)` with:
+
+```dart
+WebDatabase.withStorage(MoorWebStorage.indexedDbIfSupported(name))
+```
+
+Moor will automatically migrate data from local storage to `IndexeDb` when it is available.

moor/lib/moor_web.dart

@@ -8,6 +8,7 @@ library moor_web;
 import 'dart:async';
 import 'dart:html';
 import 'dart:indexed_db';
+import 'dart:js';
 
 import 'package:meta/meta.dart';
 

moor/lib/src/web/storage.dart

@@ -29,9 +29,30 @@ abstract class MoorWebStorage {
   /// This implementation is significantly faster than the default
   /// implementation in local storage. Browsers also tend to allow more data
   /// to be saved in IndexedDB.
+  ///
+  /// When the [migrateFromLocalStorage] parameter (defaults to `true`) is set,
+  /// old data saved using the default [MoorWebStorage] will be migrated to the
+  /// IndexedDB based implementation. This parameter can be turned off for
+  /// applications that never used the local storage implementation as a small
+  /// performance improvement.
+  ///
   /// However, older browsers might not support IndexedDB.
   @experimental
-  factory MoorWebStorage.indexedDb(String name) = _IndexedDbStorage;
+  factory MoorWebStorage.indexedDb(String name,
+      {bool migrateFromLocalStorage}) = _IndexedDbStorage;
+
+  /// Uses [MoorWebStorage.indexedDb] if the current browser supports it.
+  /// Otherwise, falls back to the local storage based implementation.
+  factory MoorWebStorage.indexedDbIfSupported(String name) {
+    return supportsIndexedDb
+        ? MoorWebStorage.indexedDb(name)
+        : MoorWebStorage(name);
+  }
+
+  /// Attempts to check whether the current browser supports the
+  /// [MoorWebStorage.indexedDb] storage implementation.
+  static bool get supportsIndexedDb =>
+      IdbFactory.supported && context.hasProperty('FileReader');
 }
 
 abstract class _CustomSchemaVersionSave implements MoorWebStorage {
@@ -39,11 +60,27 @@ abstract class _CustomSchemaVersionSave implements MoorWebStorage {
   set schemaVersion(int value);
 }
 
+String _persistenceKeyForLocalStorage(String name) {
+  return 'moor_db_str_$name';
+}
+
+String _legacyVersionKeyForLocalStorage(String name) {
+  return 'moor_db_version_$name';
+}
+
+Uint8List /*?*/ _restoreLocalStorage(String name) {
+  final raw = window.localStorage[_persistenceKeyForLocalStorage(name)];
+  if (raw != null) {
+    return bin2str.decode(raw);
+  }
+  return null;
+}
+
 class _LocalStorageImpl implements MoorWebStorage, _CustomSchemaVersionSave {
   final String name;
 
-  String get _persistenceKey => 'moor_db_str_$name';
+  String get _persistenceKey => _persistenceKeyForLocalStorage(name);
-  String get _versionKey => 'moor_db_version_$name';
+  String get _versionKey => _legacyVersionKeyForLocalStorage(name);
 
   const _LocalStorageImpl(this.name);
 
@@ -69,11 +106,7 @@ class _LocalStorageImpl implements MoorWebStorage, _CustomSchemaVersionSave {
 
   @override
   Future<Uint8List> restore() async {
-    final raw = window.localStorage[_persistenceKey];
+    return _restoreLocalStorage(name);
-    if (raw != null) {
-      return bin2str.decode(raw);
-    }
-    return null;
   }
 
   @override
@@ -89,21 +122,33 @@ class _IndexedDbStorage implements MoorWebStorage {
   static const _objectStoreName = 'moor_databases';
 
   final String name;
+  final bool migrateFromLocalStorage;
 
   Database _database;
 
-  _IndexedDbStorage(this.name);
+  _IndexedDbStorage(this.name, {this.migrateFromLocalStorage = true});
 
   @override
   Future<void> open() async {
+    var wasCreated = false;
+
     _database = await window.indexedDB.open(
       _objectStoreName,
       version: 1,
       onUpgradeNeeded: (event) {
         final database = event.target.result as Database;
+
         database.createObjectStore(_objectStoreName);
+        wasCreated = true;
       },
     );
+
+    if (migrateFromLocalStorage && wasCreated) {
+      final fromLocalStorage = _restoreLocalStorage(name);
+      if (fromLocalStorage != null) {
+        await store(fromLocalStorage);
+      }
+    }
   }
 
   @override

moor/test/web/local_storage_to_indexed_db_test.dart

@@ -0,0 +1,46 @@
+@TestOn('browser')
+import 'dart:convert';
+
+import 'package:moor/moor.dart';
+import 'package:moor/moor_web.dart';
+import 'package:test/test.dart';
+
+final _allBytes = Uint8List.fromList(List.generate(256, (index) => index));
+
+void main() {
+  test('can migrate from local storage to IndexedDb', () async {
+    const local = MoorWebStorage('name');
+    final idb = MoorWebStorage.indexedDb('name');
+
+    await local.open();
+    await local.store(_allBytes);
+    await local.close();
+
+    await idb.open();
+    final restored = await idb.restore();
+    await idb.close();
+
+    expect(restored, _allBytes);
+  });
+
+  test('does not migrate when idb database already exists', () async {
+    final otherPayload = Uint8List.fromList(utf8.encode('hello world'));
+
+    const local = MoorWebStorage('name');
+    final idb = MoorWebStorage.indexedDb('name');
+
+    await idb.open();
+    await idb.store(otherPayload);
+    await idb.close();
+
+    await local.open();
+    await local.store(_allBytes);
+    await local.close();
+
+    await idb.open();
+    final restored = await idb.restore();
+    await idb.close();
+
+    expect(restored, otherPayload);
+  });
+}