UniqueTogether for EventParticipants

src/core/models/events.py

@@ -331,6 +331,9 @@ class EventParticipant(models.Model):
         help_text=_('EventParticipant__personal_comment__help'),
         verbose_name=_('EventParticipant__personal_comment'))
 
+    class Meta:
+        unique_together = ['participant', 'event', 'role']
+
     def clean(self, *args, **kwargs):
         # verify that the participant is a member of the event's conference
         try: