API to close databases, integration test that saves data

extras/integration_tests/tests/lib/database/database.dart

@@ -121,6 +121,10 @@ class Database extends _$Database {
     return (select(users)..where((u) => u.id.equals(id))).watchSingle();
   }
 
+  Future<int> writeUser(Insertable<User> user) {
+    return into(users).insert(user);
+  }
+
   Future<void> makeFriends(User a, User b, {bool goodFriends}) async {
     var friendsValue = const Value<bool>.absent();
     if (goodFriends != null) {

extras/integration_tests/tests/lib/suite/migrations.dart

@@ -1,4 +1,5 @@
 import 'package:test/test.dart';
+import 'package:tests/data/sample_data.dart';
 import 'package:tests/database/database.dart';
 
 import 'suite.dart';
@@ -11,4 +12,16 @@ void migrationTests(TestExecutor executor) {
     final count = await database.userCount();
     expect(count.single.cOUNTid, 3);
   });
+
+  test('saves and restores database', () async {
+    var database = Database(executor.createExecutor(), schemaVersion: 1);
+    await database.writeUser(People.florian);
+    await database.close();
+
+    database = Database(executor.createExecutor(), schemaVersion: 2);
+
+    // the 3 initial users plus People.florian
+    final count = await database.userCount();
+    expect(count.single.cOUNTid, 4);
+  });
 }

moor/lib/src/runtime/database.dart

@@ -331,4 +331,9 @@ abstract class GeneratedDatabase extends DatabaseConnectionUser
       });
     }
   }
+
+  /// Closes this database and releases associated resources.
+  Future<void> close() async {
+    await executor.close();
+  }
 }

moor/lib/src/runtime/executor/executor.dart

@@ -48,6 +48,13 @@ abstract class QueryExecutor {
 
   /// Starts a [TransactionExecutor].
   TransactionExecutor beginTransaction();
+
+  /// Closes this database connection and releases all resources associated with
+  /// it. Implementations should also handle [close] calls in a state where the
+  /// database isn't open.
+  Future<void> close() async {
+    // no-op per default for backwards compatibility
+  }
 }
 
 /// A statement that should be executed in a batch. Used internally by moor.

moor/lib/src/web/sql_js.dart

@@ -101,6 +101,10 @@ class SqlJsDatabase {
   Uint8List export() {
     return _obj.callMethod('export') as Uint8List;
   }
+
+  void close() {
+    _obj.callMethod('close');
+  }
 }
 
 class PreparedStatement {

moor/lib/src/web/web_db.dart

@@ -87,6 +87,13 @@ class _WebDelegate extends DatabaseDelegate {
     return _handlePotentialUpdate();
   }
 
+  @override
+  Future<void> close() {
+    _storeDb();
+    _db?.close();
+    return Future.value();
+  }
+
   /// Saves the database if the last statement changed rows. As a side-effect,
   /// saving the database resets the `last_insert_id` counter in sqlite.
   Future<int> _handlePotentialUpdate() {