How to pass an object as an argument in order to store data to a database?

I am relatively new to Android and I'm a little bit stuck as fighting my way through databases, so any guidelines are much appreciated! Here it goes~

    //Random Fragment that inserts data to the databaase
    mWorkoutData = new WorkoutData();
    mDBTools = new DBTools(getActivity());

    HashMap<String, String> queryValuesMap =  new HashMap<String, String>();

    queryValuesMap.put("comments", mWorkoutData.getComments());

    mDBTools.insertWorkoutData(queryValuesMap);

The WorkoutData is the model class, however it does not manage to insert any data to the database while in case I pass an Edittext for example as an argument everything is fine!

Any guidelines or insights on how to solve this would be much appreciated!