Fix n+1 query on staff deleted message logs page

Author: ChrisLovering

pydis_site/apps/api/models/bot/user.py

@@ -1,3 +1,5 @@
+from functools import lru_cache
+
 from django.contrib.postgres.fields import ArrayField
 from django.core.validators import MaxValueValidator, MinValueValidator
 from django.db import models
@@ -70,14 +72,20 @@ def __str__(self):
             return f"{self.name}#{self.discriminator:04d}"
         return self.name
 
+    @staticmethod
+    @lru_cache(maxsize=256)
+    def _get_roles(role_ids: tuple[int, ...]) -> list[Role]:
+        """Fetch the given roles, cached to avoid refetching the same roles for every user."""
+        return list(Role.objects.filter(id__in=role_ids))
+
     @property
     def top_role(self) -> Role:
         """
         Attribute that returns the user's top role.
 
         This will fall back to the Developers role if the user does not have any roles.
         """
-        roles = Role.objects.filter(id__in=self.roles)
+        roles = self._get_roles(tuple(sorted(self.roles)))
         if not roles:
             return Role.objects.get(name="Developers")
         return max(roles)

pydis_site/apps/api/signals.py

@@ -1,4 +1,4 @@
-from django.db.models.signals import post_delete
+from django.db.models.signals import post_delete, post_save
 from django.dispatch import receiver
 
 from pydis_site.apps.api.models.bot import Role, User
@@ -10,3 +10,10 @@ def delete_role_from_user(sender: Role, instance: Role, **kwargs) -> None:
     for user in User.objects.filter(roles__contains=[instance.id]):
         del user.roles[user.roles.index(instance.id)]
         user.save()
+
+
+@receiver(signal=post_save, sender=Role)
+@receiver(signal=post_delete, sender=Role)
+def clear_top_role_cache(sender: Role, **kwargs) -> None:
+    """Clear the cached role lookups used by `User.top_role` when a role changes."""
+    User._get_roles.cache_clear()

pydis_site/apps/staff/views.py

@@ -1,5 +1,7 @@
+from django.db.models import Prefetch
 from django.views.generic.detail import DetailView
 
+from pydis_site.apps.api.models.bot.deleted_message import DeletedMessage
 from pydis_site.apps.api.models.bot.message_deletion_context import MessageDeletionContext
 
 
@@ -9,3 +11,9 @@ class LogView(DetailView):
     model = MessageDeletionContext
     context_object_name = "deletion_context"
     template_name = "staff/logs.html"
+    queryset = MessageDeletionContext.objects.select_related("actor").prefetch_related(
+        Prefetch(
+            "deletedmessage_set",
+            queryset=DeletedMessage.objects.select_related("author"),
+        ),
+    )