Always got TDB model size = 0

Hi, Jena experts:

Jena v2.10.1 on Windows 7.

(1) Run TDB loader: loadRDF.cmd myDir myRdfXML.xml.

(2) Create a TDB sitting on "myDir":
model = TDBFactory.createDataset("myDir").getDefaultModel();

However, model.size() will always give 0! And any query won't return
anything!

If I start Fuseki on "myDir": fuseki-server.bat --loc myDir
--home=<fuseki_home> /myDir, I can run the same query and return rows.

Is there anything wrong with my code in step (2)?

Thanks a lot for your help!!
- Charles