List each member only once in Registration admin

Previously `Member`s with multiple `Membership`s were listed

website/events/admin.py

@@ -182,4 +182,6 @@ class RegistrationAdmin(DoNextModelAdmin):
             if request.GET.get('event_pk'):
                 kwargs['queryset'] = models.Event.objects.filter(
                     pk=int(request.GET['event_pk']))
+        elif db_field.name == 'member':
+            kwargs['queryset'] = Member.active_members.all()
         return super().formfield_for_foreignkey(db_field, request, **kwargs)

website/members/models.py

@@ -24,7 +24,8 @@ class ActiveMemberManager(models.Manager):
         return (super().get_queryset()
                 .exclude(user__membership=None)
                 .filter(Q(user__membership__until__isnull=True) |
-                        Q(user__membership__until__gt=timezone.now().date())))
+                        Q(user__membership__until__gt=timezone.now().date()))
+                .distinct())
 
     def with_birthdays_in_range(self, from_date, to_date):
         queryset = self.get_queryset().filter(birthday__lte=to_date)