Can't use wrapper with combobox to view|save with non integer key value

mapper->addMapping(typeComboBox, 2, "currentIndex") works if I want save index of the value. But what if my key value is not integer?
I works with database table where primary key is GUID and want to map values by it.
And I don't need to save current text of combobox, I need to save key value mapper->addMapping(typeComboBox, 2, "currentText") doesn't work too