API: Fix duplicate results when filtering orders

src/pretix/api/views/order.py

@@ -105,9 +105,9 @@ with scopes_disabled():
         subevent_after = django_filters.IsoDateTimeFilter(method='subevent_after_qs')
         subevent_before = django_filters.IsoDateTimeFilter(method='subevent_before_qs')
         search = django_filters.CharFilter(method='search_qs')
-        item = django_filters.CharFilter(field_name='all_positions', lookup_expr='item_id')
-        variation = django_filters.CharFilter(field_name='all_positions', lookup_expr='variation_id')
-        subevent = django_filters.CharFilter(field_name='all_positions', lookup_expr='subevent_id')
+        item = django_filters.CharFilter(field_name='all_positions', lookup_expr='item_id', distinct=True)
+        variation = django_filters.CharFilter(field_name='all_positions', lookup_expr='variation_id', distinct=True)
+        subevent = django_filters.CharFilter(field_name='all_positions', lookup_expr='subevent_id', distinct=True)
 
         class Meta:
             model = Order

src/tests/api/test_orders.py

@@ -324,6 +324,21 @@ def test_order_list_filter_subevent_date(token_client, organizer, event, order,
     assert resp.status_code == 200
     assert [res] == resp.data['results']
 
+    # Test distinct-ness of results
+    with scopes_disabled():
+        OrderPosition.objects.create(
+            order=order,
+            item=item,
+            variation=None,
+            price=Decimal("23"),
+            canceled=False,
+            positionid=3,
+            subevent=subevent,
+        )
+    resp = token_client.get(
+        '/api/v1/organizers/{}/events/{}/orders/?subevent={}'.format(organizer.slug, event.slug, subevent.pk))
+    assert len(resp.data['results']) == 1
+
 
 @pytest.mark.django_db
 def test_order_list(token_client, organizer, event, order, item, taxrule, question):