Cache user-specific ratings

bookwyrm/models/status.py

@@ -3,6 +3,7 @@ from dataclasses import MISSING
 import re
 
 from django.apps import apps
+from django.core.cache import cache
 from django.core.exceptions import PermissionDenied
 from django.core.validators import MaxValueValidator, MinValueValidator
 from django.db import models
@@ -373,6 +374,11 @@ class Review(BookStatus):
     activity_serializer = activitypub.Review
     pure_type = "Article"
 
+    def save(self, *args, **kwargs):
+        """clear rating caches"""
+        cache.delete(f"book-rating-{self.book.parent_work.id}-*")
+        super().save(*args, **kwargs)
+
 
 class ReviewRating(Review):
     """a subtype of review that only contains a rating"""

bookwyrm/templatetags/bookwyrm_tags.py

@@ -13,10 +13,15 @@ register = template.Library()
 @register.filter(name="rating")
 def get_rating(book, user):
     """get the overall rating of a book"""
-    queryset = models.Review.privacy_filter(user).filter(
+    return cache.get_or_set(
-        book__parent_work__editions=book
+        f"book-rating-{book.parent_work.id}-{user.id}",
+        lambda u, b: models.Review.privacy_filter(u)
+        .filter(book__parent_work__editions=b)
+        .aggregate(Avg("rating"))["rating__avg"],
+        user,
+        book,
+        timeout=15552000,
     )
-    return queryset.aggregate(Avg("rating"))["rating__avg"]
 
 
 @register.filter(name="user_rating")