Build: Denormalize latest build for projects (#12392)

Sorting by the last build project is expensive, as the query is done for
each project (even if paginated, since the order applies to all
projects). For comparison, here are some numbers with data from
production

```
# Ordering by name
145 ms ± 446 μs per loop (mean ± std. dev. of 5 runs, 5 loops each)

# Ordering by max(builds_date)
4.37 s ± 254 ms per loop (mean ± std. dev. of 5 runs, 5 loops each)
```

The migration is going to take some time to run, I imagine... but should
be worth it for a snappier dashboard.

Author: stsewd

readthedocs/builds/apps.py

@@ -15,3 +15,4 @@ class Config(AppConfig):
 
     def ready(self):
         import readthedocs.builds.tasks  # noqa
+        import readthedocs.builds.signals_receivers  # noqa

readthedocs/builds/signals_receivers.py

@@ -0,0 +1,20 @@
+"""
+Receiver signals for the Builds app.
+
+NOTE: Done in a separate file to avoid circular imports.
+"""
+
+from django.db.models.signals import post_save
+from django.dispatch import receiver
+
+from readthedocs.builds.models import Build
+from readthedocs.projects.models import Project
+
+
+@receiver(post_save, sender=Build)
+def update_latest_build_for_project(sender, instance, created, **kwargs):
+    """When a build is created, update the latest build for the project."""
+    if created:
+        Project.objects.filter(pk=instance.project_id).update(
+            latest_build=instance,
+        )

readthedocs/builds/tests/test_trigger_build.py

@@ -90,3 +90,25 @@ def test_not_cancel_old_finished_build(self, update_docs_task, cancel_build, sta
         assert builds_count_before == builds_count_after - 1
         assert update_docs_task.signature.called
         assert update_docs_task.signature().apply_async.called
+
+    @mock.patch("readthedocs.core.utils.cancel_build")
+    @mock.patch("readthedocs.projects.tasks.builds.update_docs_task")
+    def test_update_latest_build_on_trigger(self, update_docs_task, cancel_build):
+        assert self.project.builds.count() == 0
+        assert self.project.latest_build is None
+        _, build = trigger_build(
+            project=self.project,
+            version=self.version,
+        )
+
+        self.project.refresh_from_db()
+        assert self.project.builds.count() == 1
+        assert self.project.latest_build == build
+
+        _, build = trigger_build(
+            project=self.project,
+            version=self.version,
+        )
+        self.project.refresh_from_db()
+        assert self.project.builds.count() == 2
+        assert self.project.latest_build == build

readthedocs/projects/admin.py

@@ -240,7 +240,7 @@ class ProjectAdmin(ExtraSimpleHistoryAdmin):
         "feature_flags",
         "matching_spam_rules",
     )
-    raw_id_fields = ("users", "main_language_project", "remote_repository")
+    raw_id_fields = ("users", "main_language_project", "remote_repository", "latest_build")
     actions = [
         "ban_owner",
         "run_spam_rule_checks",

readthedocs/projects/migrations/0153_project_latest_build.py

@@ -0,0 +1,42 @@
+# Generated by Django 5.2.3 on 2025-08-11 21:09
+
+import django.db.models.deletion
+from django.db import migrations
+from django.db import models
+from django_safemigrate import Safe
+
+
+class Migration(migrations.Migration):
+    safe = Safe.before_deploy()
+    dependencies = [
+        ("builds", "0064_healthcheck"),
+        ("projects", "0152_create_gh_app_integration"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="historicalproject",
+            name="latest_build",
+            field=models.ForeignKey(
+                blank=True,
+                db_constraint=False,
+                null=True,
+                on_delete=django.db.models.deletion.DO_NOTHING,
+                related_name="+",
+                to="builds.build",
+                verbose_name="Latest build",
+            ),
+        ),
+        migrations.AddField(
+            model_name="project",
+            name="latest_build",
+            field=models.OneToOneField(
+                blank=True,
+                null=True,
+                on_delete=django.db.models.deletion.SET_NULL,
+                related_name="+",
+                to="builds.build",
+                verbose_name="Latest build",
+            ),
+        ),
+    ]

readthedocs/projects/migrations/0154_set_latest_build.py

@@ -0,0 +1,24 @@
+# Generated by Django 5.2.3 on 2025-08-11 21:16
+
+from django.db import migrations
+from django_safemigrate import Safe
+
+
+def forward(apps, schema_editor):
+    Project = apps.get_model("projects", "Project")
+    for project in Project.objects.all().iterator():
+        latest_build = project.builds.order_by("-date").first()
+        if latest_build:
+            project.latest_build = latest_build
+            project.save()
+
+
+class Migration(migrations.Migration):
+    safe = Safe.after_deploy()
+    dependencies = [
+        ("projects", "0153_project_latest_build"),
+    ]
+
+    operations = [
+        migrations.RunPython(forward),
+    ]

readthedocs/projects/models.py

@@ -634,6 +634,17 @@ class Project(models.Model):
         null=True,
     )
 
+    # Denormalized fields
+    latest_build = models.OneToOneField(
+        "builds.Build",
+        verbose_name=_("Latest build"),
+        # No reverse relation needed.
+        related_name="+",
+        on_delete=models.SET_NULL,
+        null=True,
+        blank=True,
+    )
+
     # Property used for storing the latest build for a project when prefetching
     LATEST_BUILD_CACHE = "_latest_build"