Working with virtual attributes is definitely not the same thing. Virtual attributes are not saved in the database, which makes it impossible to search or sort on virtual attributes.
Currently, it's no problem to work with associations one level deep. Unfortunately, showing associated objects more than one level deep in a form is not possible yet... (but, work in progress, we have to wait until the 2.5 version is released).
For now, I have a solution which isn't smooth and proper at all: just add an extra association and make it one level deep. Policy - Reminder, set this association based on the associations Policy - Open Invoice and Open Invoice - Reminder by using microflow.
In our upcoming 2.5 release you can use attributes from objects associated to the current object via multiple steps. This holds for input fields in dataviews, columns in datagrids, and searchfields in datagrids.