I rechecked and setData() returns true.
My goal is to make a computed column of something related to that database and display it.
I'm not at all trying to modify the underlying database..

My plan was to load the desired table from the database to a model, display it, then add one more column to the model, and fill it with whatever I want(it was like this in ado.Net). Your reply suggest that there is a stronger connection between the db and the model.
I recently started to learn the model/view part of Qt and probably went the wrong way....

So how can I do something like this?