Store all check-in attempts, not only successful ones (#2074)

src/pretix/base/models/orders.py

@@ -2054,6 +2054,14 @@ class OrderPosition(AbstractPosition):
     def sort_key(self):
         return self.addon_to.positionid if self.addon_to else self.positionid, self.addon_to_id or 0
 
+    @property
+    def checkins(self):
+        """
+        Related manager for all successful checkins. Use ``all_checkins`` instead if you want
+        canceled positions as well.
+        """
+        return self.all_checkins(manager='objects')
+
     @property
     def generate_ticket(self):
         if self.item.generate_tickets is not None: