[Answer]-Efficiently Populating Dropdown List: Javascript vs Database (Mysql-Django)

For the sake of usability I would update the select boxes using Ajax calls.

Another benefit from choosing this approach would be that your application logic is mostly kept server side, which in most cases is easier to write tests for.

You could populate the first select box by querying in your view and passing the results down to your template. If you disable the other 2 select boxes you can active/populate them after the 1 one is selected through an ajax call.