Fix #1759: order import increasing positionids (#1776)

src/pretix/base/services/orderimport.py

@@ -103,7 +103,7 @@ def import_orders(event: Event, fileid: str, settings: dict, locale: str, user)
                     order._address.name_parts = {'_scheme': event.settings.name_scheme}
                     orders.append(order)
 
-                position = OrderPosition()
+                position = OrderPosition(positionid=len(order._positions) + 1)
                 position.attendee_name_parts = {'_scheme': event.settings.name_scheme}
                 position.meta_info = {}
                 order._positions.append(position)

src/tests/base/test_orderimport.py

@@ -130,6 +130,7 @@ def test_import_as_one_order(user, event, item):
     assert event.orders.count() == 1
     o = event.orders.get()
     assert o.positions.count() == 3
+    assert set(pos.positionid for pos in o.positions.all()) == {1, 2, 3}
 
 
 @pytest.mark.django_db