Web: Flush IndexedDB after transactions and RETURNING statements (#3865)

The COMMIT statement runs while isInTransaction is still set, so changes
made in a transaction were never flushed. Check sqlite3's autocommit state
instead, and also flush after selects since they can write too.

Author: sawongam

drift/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 2.35.1-dev
+
+- Web: Fix writes made in transactions or through `RETURNING` statements not being persisted to IndexedDB (#3864).
+
 ## 2.35.0
 
 - Add support for FTS5 queries in the Dart API: `match`, `matchExp`, `highlight`, `snippet`, `bm25` and `rank` are now available as extension methods on FTS5 tables from `package:drift/extensions/fts5.dart` (#3843).

drift/lib/wasm.dart

@@ -359,12 +359,27 @@ class _WasmDelegate extends Sqlite3Delegate<CommonDatabase> {
     await _fileSystem?.flush();
   }
 
+  Future<void> _flushIfOutsideOfTransaction() async {
+    // Checking isInTransaction isn't enough here: The flag is only reset after
+    // the COMMIT statement has completed, so relying on it would never flush
+    // the changes made in a transaction.
+    if (database.autocommit) {
+      await _flush();
+    }
+  }
+
   Future _runWithArgs(String statement, List<Object?> args) async {
     runWithArgsSync(statement, args);
+    await _flushIfOutsideOfTransaction();
+  }
 
-    if (!isInTransaction) {
-      await _flush();
-    }
+  @override
+  Future<QueryResult> runSelect(String statement, List<Object?> args) async {
+    final result = await super.runSelect(statement, args);
+    // Selects can write too (e.g. with a RETURNING clause). Flushing without
+    // pending writes is cheap.
+    await _flushIfOutsideOfTransaction();
+    return result;
   }
 
   @override
@@ -387,10 +402,7 @@ class _WasmDelegate extends Sqlite3Delegate<CommonDatabase> {
   @override
   Future<void> runBatched(BatchedStatements statements) async {
     runBatchSync(statements);
-
-    if (!isInTransaction) {
-      await _flush();
-    }
+    await _flushIfOutsideOfTransaction();
   }
 
   @override

extras/integration_tests/web_wasm/lib/driver.dart

@@ -166,6 +166,14 @@ class DriftWebDriver {
     await driver.executeAsync('insert("", arguments[0])', []);
   }
 
+  Future<void> insertInTransaction() async {
+    await driver.executeAsync('insert_in_transaction("", arguments[0])', []);
+  }
+
+  Future<void> insertReturning() async {
+    await driver.executeAsync('insert_returning("", arguments[0])', []);
+  }
+
   Future<void> runExclusiveBlock() async {
     await driver.executeAsync('do_exclusive("", arguments[0])', []);
   }

extras/integration_tests/web_wasm/test/drift_wasm_test.dart

@@ -290,6 +290,21 @@ final class _TestConfiguration {
             await driver.openDatabase();
             expect(await driver.hasTable, isFalse);
           });
+
+          test('persists writes from transactions and RETURNING', () async {
+            await driver.openDatabase(implementation: entry);
+            await driver.insertInTransaction();
+            await driver.insertReturning();
+            expect(await driver.amountOfRows, 2);
+
+            // No delay before reloading: the writes must have been persisted
+            // by the time they complete.
+            await driver.driver.refresh();
+            await driver.waitReady();
+
+            await driver.openDatabase(implementation: entry);
+            expect(await driver.amountOfRows, 2);
+          });
         }
 
         group(

extras/integration_tests/web_wasm/web/main.dart

@@ -50,6 +50,22 @@ void main() {
     return null;
   });
   _addCallbackForWebDriver('insert', _insert);
+  _addCallbackForWebDriver('insert_in_transaction', (arg) async {
+    final db = openedDatabase!;
+    await db.transaction(() async {
+      await db
+          .into(db.testTable)
+          .insert(TestTableCompanion.insert(content: 'from transaction'));
+    });
+    return null;
+  });
+  _addCallbackForWebDriver('insert_returning', (arg) async {
+    final db = openedDatabase!;
+    await db
+        .into(db.testTable)
+        .insertReturning(TestTableCompanion.insert(content: 'returning'));
+    return null;
+  });
   _addCallbackForWebDriver('get_rows', _getRows);
   _addCallbackForWebDriver('has_table', _hasTables);
   _addCallbackForWebDriver('wait_for_update', _waitForUpdate);