Add default ordering for Invoice and OrderPosition

src/pretix/base/models/invoices.py

@@ -122,6 +122,7 @@ class Invoice(models.Model):
 
     class Meta:
         unique_together = ('event', 'invoice_no')
+        ordering = ('invoice_no',)
 
 
 class InvoiceLine(models.Model):

src/pretix/base/models/orders.py

@@ -479,6 +479,7 @@ class OrderPosition(AbstractPosition):
     class Meta:
         verbose_name = _("Order position")
         verbose_name_plural = _("Order positions")
+        ordering = ("positionid",)
 
     @classmethod
     def transform_cart_positions(cls, cp: List, order) -> list: