watch method

Implementation

Stream<List<MapChangeNotification<UserId, Credentials?>>> watch() {
  return stream((db) {
    final stmt = db.select(db.tokens);
    return stmt
        .watch()
        .map((rows) => rows.map(_CredentialsDb.fromDb).toList())
        .map((i) => {for (var e in i) e.userId: e})
        .changes();
  });
}