Use multiple caches

- set up a 5-minute memory cache
- use a back-up 24-hour db cache

api/buildings/models.py

@@ -6,7 +6,6 @@
 
 import PIL.Image
 from django.conf import settings
-from django.core.cache import cache
 from django.core.exceptions import ValidationError
 from django.core.files.uploadedfile import InMemoryUploadedFile
 from django.db import models
@@ -15,8 +14,9 @@
 from django.utils.safestring import mark_safe
 from django.utils.translation import get_language, gettext_lazy as _
 
+from seismic_site.caching import delete_from_cache
+
 BUILDINGS_LISTING_CACHE_KEY = "all_buildings_listing"
-BUILDINGS_LISTING_CACHE_TIMEOUT = 60 * 60 * 24  # 24 hours
 
 
 class SeismicCategoryChoice(Enum):
@@ -103,7 +103,7 @@ def bulk_create(self, *args, **kwargs):
         super().bulk_create(self, *args, **kwargs)
 
         Statistic.update_statistics()
-        cache.delete(BUILDINGS_LISTING_CACHE_KEY)
+        delete_from_cache(BUILDINGS_LISTING_CACHE_KEY)
 
 
 class ApprovedBuilding(models.Manager):

api/buildings/signals.py

@@ -1,7 +1,7 @@
-from django.core.cache import cache
 from django.db.models.signals import post_save
 from django.dispatch import receiver
 
+from seismic_site.caching import delete_from_cache
 from .models import BUILDINGS_LISTING_CACHE_KEY, Building, Statistic
 
 
@@ -10,7 +10,7 @@ def refresh_cache(instance: Building, **kwargs):
     if not isinstance(instance, Building):
         return
 
-    cache.delete(BUILDINGS_LISTING_CACHE_KEY)
+    delete_from_cache(BUILDINGS_LISTING_CACHE_KEY)
 
 
 @receiver(post_save, sender=Building)

api/buildings/views.py

@@ -2,16 +2,15 @@
 
 from django.conf import settings
 from django.contrib.postgres.search import TrigramSimilarity
-from django.core.cache import cache
 from drf_spectacular.utils import OpenApiParameter, extend_schema
 from rest_framework import permissions, status, viewsets
 from rest_framework.decorators import action, api_view, permission_classes
 from rest_framework.response import Response
 from rest_framework.throttling import AnonRateThrottle
 
+from seismic_site.caching import get_from_cache, set_to_cache
 from .models import (
     BUILDINGS_LISTING_CACHE_KEY,
-    BUILDINGS_LISTING_CACHE_TIMEOUT,
     Building,
     BuildingProximalUtilities,
     BuildingWorkPerformed,
@@ -49,7 +48,7 @@ def list(self, request, *args, **kwargs):
         """
         nonexistent = object()  # sentinel
 
-        cached_data: List = cache.get(BUILDINGS_LISTING_CACHE_KEY, nonexistent)
+        cached_data: List = get_from_cache(BUILDINGS_LISTING_CACHE_KEY, nonexistent)
 
         if cached_data is nonexistent:
             queryset = self.filter_queryset(self.get_queryset())
@@ -62,7 +61,7 @@ def list(self, request, *args, **kwargs):
             serializer = self.get_serializer(queryset, many=True)
             cached_data = serializer.data
 
-            cache.set(BUILDINGS_LISTING_CACHE_KEY, cached_data, timeout=BUILDINGS_LISTING_CACHE_TIMEOUT)
+            set_to_cache(BUILDINGS_LISTING_CACHE_KEY, cached_data)
 
         return Response(cached_data)
 
@@ -145,10 +144,7 @@ class WorkPerformedViewSet(viewsets.ReadOnlyModelViewSet):
     serializer_class = WorkPerformedSerializer
 
 
-@extend_schema(
-    request=StatisticSerializer,
-    responses=None  # TODO: is it really None?
-)
+@extend_schema(request=StatisticSerializer, responses=None)  # TODO: is it really None?
 @api_view(["GET"])
 @permission_classes((permissions.AllowAny,))
 def statistics(request):

api/seismic_site/caching.py

@@ -0,0 +1,24 @@
+from typing import Any
+
+from django.core.cache import caches
+
+
+def get_from_cache(data_key: str, default: Any = object()) -> Any:
+    cached_data = caches["memory"].get(data_key, default)
+
+    if cached_data is default:
+        cached_data = caches["default"].get(data_key, default)
+        if cached_data is not default:
+            caches["memory"].set(data_key, cached_data)
+
+    return cached_data
+
+
+def set_to_cache(data_key: str, data: Any, timeout: int = None) -> None:
+    for cache in caches.all():
+        cache.set(data_key, data, timeout=timeout)
+
+
+def delete_from_cache(data_key: str) -> None:
+    for cache in caches.all():
+        cache.delete(data_key)

api/seismic_site/settings/base.py

@@ -142,9 +142,15 @@
 
 CACHES = {
     "default": {
+        "BACKEND": "django.core.cache.backends.db.DatabaseCache",
+        "LOCATION": "seismic_cache_table",
+        "TIMEOUT": 60 * 60 * 24,  # 24 hours
+    },
+    "memory": {
         "BACKEND": "django.core.cache.backends.locmem.LocMemCache",
         "LOCATION": "unique-snowflake",
-    }
+        "TIMEOUT": 60 * 5,  # 5 minutes
+    },
 }
 
 # Internationalization