paperwork: Use window functions for CertificationVersion is_current/is_latest

This should be a lot more efficient, and is much cleaner code too

paperwork/models.py

@@ -4,7 +4,8 @@ from typing import TypedDict, TYPE_CHECKING, Optional
 
 from semver import VersionInfo
 from django.db import models
-from django.db.models import OuterRef, Q, ExpressionWrapper, Subquery
+from django.db.models import Q, Window
+from django.db.models.functions import FirstValue
 from django.conf import settings
 from django.core.validators import RegexValidator
 from django_stubs_ext import WithAnnotations
@@ -139,18 +140,23 @@ class CertificationVersionAnnotations(TypedDict):
 
 class CertificationVersionManager(models.Manager["CertificationVersion"]):
     def get_queryset(self) -> models.QuerySet["CertificationVersion"]:
-        qs = super().get_queryset()
-        latest = qs.filter(definition__pk=OuterRef("definition__pk")).reverse()
-        return qs.annotate(
-            is_latest=ExpressionWrapper(
-                Q(pk=Subquery(latest.values("pk")[:1])),
-                output_field=models.BooleanField(),
-            ),
-            # TODO: should do a more correct comparison than just major version
-            is_current=ExpressionWrapper(
-                Q(major=Subquery(latest.values("major")[:1])),
-                output_field=models.BooleanField(),
-            ),
+        window = {
+            "partition_by": "definition",
+            "order_by": [
+                "-major",
+                "-minor",
+                "-patch",
+                "-prerelease",
+            ],
+        }
+        return (
+            super()
+            .get_queryset()
+            .annotate(
+                is_latest=Q(pk=Window(FirstValue("pk"), **window)),
+                # TODO: should do a more correct comparison than just major version
+                is_current=Q(major=Window(FirstValue("major"), **window)),
+            )
         )