How to properly package in Dart?

Question

Dart

Good afternoon, I'm slowly learning Dart. I have experience in developing in Java, so I try to do it by analogy, but something confuses me. In general, the task is to make a DAO layer. I took this as a basis: www.oracle.com/technetwork/java/dataaccessobject-1...
I got the following package structure and required classes:
db/
+ sqlite
| +- SqLiteDaoFactory
+- AbstractDaoFactory AbstractDaoFactory
has a static method that returns the requested factory implementation:

static DaoFactory getDAOFactory(StorageType type) {
    switch (type) {
      case StorageType.SQLITE:
        return new SqliteDaoFactory();

      default:
        return null;
    }
  }

This gives us a circular dependency between the db/ and db/sqlite packages . Because SqliteDaoFactory inherits from AbstractDaoFactory . Something I don't really like. How to do it correctly in Dart? Putting everything in one package somehow does not really want to.
A couple of additions. An abstraction layer is needed because I plan to test different databases. Perhaps even use different implementations for different tasks. Well, I don’t like the code that I saw in Flutter articles. There, in general, all work with the database is dumped into one class.
Flutter is already somehow damn confusing compared to the same Swing, so I don’t want to get crap out of nowhere when working with the database.