Relationships with mixed data types

Are relationships with a mixed data types supported? For example:

var activity:Activity = new Activity();
var exercise:Exercise = new Exercise();
var workout:Workout = new Workout();
workout.activities = [activity, exercise];

If I try to save workout, Workout and Activity tables are created, but an Exercise table is not, and it returns an error about table generation.

I dIdn’t know if I was doing something wrong, or if it’s simply not supported.