Add start of simple module to help with caching singleton URLs

website/contrib/singleton_url/tests.py

@@ -0,0 +1,16 @@
+from django.test import TestCase
+
+from website.common.models import ContentPage
+from website.home.models import HomePage
+
+from .utils import SingletonURLCache
+
+
+class SingletonURLTestCase(TestCase):
+    def test_gets_url(self) -> None:
+        with self.assertNumQueries(2):
+            self.assertEqual(SingletonURLCache.get_url(HomePage), "http://localhost/")
+
+    def test_missing_page(self) -> None:
+        with self.assertNumQueries(1):
+            self.assertIsNone(SingletonURLCache.get_url(ContentPage))

website/contrib/singleton_url/utils.py

@@ -0,0 +1,32 @@
+from typing import Type
+
+from django.core.cache import cache
+from django.http.request import HttpRequest
+from wagtail.models import Page
+
+
+class SingletonURLCache:
+    @classmethod
+    def get_url_cache_key(cls, model: Type[Page]) -> str:
+        return f"singleton_url_{model.__name__}"
+
+    @classmethod
+    def get_url(
+        cls, model: Type[Page], request: HttpRequest | None = None
+    ) -> str | None:
+        cache_key = cls.get_url_cache_key(model)
+
+        url = cache.get(cache_key)
+
+        if url is None:
+            # `.first` is marginally more efficient than `.get`
+            page = Page.objects.type(model).first()
+
+            if page is None:
+                return None
+
+            url = page.get_full_url(request)
+
+            cache.set(cache_key, url, 86400)
+
+        return url

website/contrib/singleton_url/wagtail_hooks.py

@@ -0,0 +1,16 @@
+from django.core.cache import cache
+from wagtail import hooks
+
+from website.common.utils import get_page_models
+
+from .utils import SingletonURLCache
+
+
+@hooks.register("after_move_page")
+def clear_singleton_url_cache(**kwargs: dict) -> None:
+    """
+    Clear all page caches, in case a parent has moved
+    """
+    cache.delete_many(
+        [SingletonURLCache.get_url_cache_key(model) for model in get_page_models()]
+    )

website/settings.py

@@ -41,6 +41,7 @@ INSTALLED_APPS = [
     "website.contrib.code_block",
     "website.contrib.mermaid_block",
     "website.contrib.unsplash",
+    "website.contrib.singleton_url",
     "wagtail.contrib.forms",
     "wagtail.contrib.redirects",
     "wagtail.contrib.modeladmin",