Improve price information

games/signals.py

@@ -0,0 +1,12 @@
+from django.db.models.signals import m2m_changed
+from django.dispatch import receiver
+from django.utils.timezone import now
+
+from games.models import Purchase
+
+
+@receiver(m2m_changed, sender=Purchase.games.through)
+def update_num_purchases(sender, instance, **kwargs):
+    instance.num_purchases = instance.games.count()
+    instance.updated_at = now()
+    instance.save(update_fields=["num_purchases"])