I am in the same situation, using a class derived from ExtendedDataModel. It's working fine when the sorting functionality is disabled.
We need this functionality and I would like the DB to do the sorting. So, I need to access something like getSortFields() and probably also need to tell the dataTable component that the sort is done 'externally'.
Why is the first post not answered? If it's not possible, than say so.
Thanks in advance
No such functionality right now
Feel free to submit that issue to Jira