Reset schema when validateDatabaseSchema() fails

[hiroshihorie]

I use Drift as a local cache for my app and I can afford to clear / recreate all data when schema changes.
How can I reset schema at launch if validateDatabaseSchema() fails and continue to run the app ?

[simolus3]

Something like this in the MigrationStrategy should work:

}, beforeOpen: (details) async {
  try {
    await validateDatabaseSchema();
  } on SchemaMismatch {
    // Delete all databases and re-create
    final migrator = createMigrator();
    final reversedEntities = allSchemaEntities.toList().reversed;

    for (final entity in reversedEntities) {
      await migrator.drop(entity);
    }

    await migrator.createAll();
  }
});

You don't need an onUpgrade callback at all in that case.

[hiroshihorie]

Thanks, so I guess I will still need to bump the schemaVersion manually.

[albertmoravec]

Just to clarify, this would only drop entities currently present in the schema, right? If I removed a table from the schema and called this code afterwards without proper migration, it would still be present?

[simolus3]

Oh right, good catch! Yes, it would only delete tables that drift is aware of. A better approach may be to to close+delete the whole database before re-opening it, but that's not really possible from the beforeOpen callback. Another option may be to run a select on select * from sqlite_schema and use that to delete everything.

[albertmoravec]

I'm personally not in the exact same situation, so I decided to delete tables manually based on sqlite_schema. Deleting the whole database file would be the best option for me, but it is not currently possible for WasmDatabase AFAIK(?)

[simolus3]

You can use WasmDatabase.probe followed by WasmProbeResult.deleteDatabase, but it's not something that could be done within a migration callback.