membershipworks: Convert EventExt.person_hours to annotation

membershipworks/models.py

@@ -4,7 +4,7 @@ from datetime import datetime
 import django.core.mail.message
 from django.conf import settings
 from django.db import models
-from django.db.models import Exists, F, OuterRef, Subquery, Sum
+from django.db.models import Exists, ExpressionWrapper, F, OuterRef, Subquery, Sum
 from django.utils import timezone
 
 
@@ -426,6 +426,11 @@ class EventExtManager(models.Manager["EventExt"]):
                     .values("d")[:1],
                     output_field=models.DurationField(),
                 ),
+                person_hours=ExpressionWrapper(
+                    ExpressionWrapper(F("duration"), models.IntegerField())
+                    * F("count"),
+                    models.DurationField(),
+                ),
             )
         )
 
@@ -448,14 +453,6 @@ class EventExt(Event):
         max_digits=13, decimal_places=4, default=0
     )
 
-    # TODO: ideally this would be a generated column or annotation,
-    #       but I couldn't get the types to work out
-    @property
-    def person_hours(self):
-        if self.duration is None:
-            return None
-        return self.count * self.duration
-
     class Meta:
         verbose_name = "event"