Count view: async slow counts

when you count, it's usually because there are many, so this
extra complication is probaly going to be required

bsmain/migrations/0002_cachedmodelcount.py

@@ -0,0 +1,32 @@
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("bsmain", "0001_initial"),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name="CachedModelCount",
+            fields=[
+                (
+                    "id",
+                    models.BigAutoField(
+                        auto_created=True,
+                        primary_key=True,
+                        serialize=False,
+                        verbose_name="ID",
+                    ),
+                ),
+                ("app_label", models.CharField(max_length=255)),
+                ("model_name", models.CharField(max_length=255)),
+                ("count", models.PositiveIntegerField()),
+                ("last_updated", models.DateTimeField(auto_now=True)),
+            ],
+            options={
+                "unique_together": {("app_label", "model_name")},
+            },
+        ),
+    ]

bsmain/models.py

@@ -18,3 +18,15 @@ class AuthToken(models.Model):
 
     def __str__(self):
         return f"AuthToken(token={self.token})"
+
+
+class CachedModelCount(models.Model):
+    """Model to cache the count of a specific model."""
+
+    app_label = models.CharField(max_length=255)
+    model_name = models.CharField(max_length=255)
+    count = models.PositiveIntegerField(null=False, blank=False)
+    last_updated = models.DateTimeField(auto_now=True)
+
+    class Meta:
+        unique_together = ('app_label', 'model_name')

bsmain/tasks.py

@@ -0,0 +1,26 @@
+from django.apps import apps
+from django.utils import timezone
+
+from snappea.decorators import shared_task
+
+from bugsink.transaction import durable_atomic, immediate_atomic
+from .models import CachedModelCount
+
+
+@shared_task
+def count_model(app_label, model_name):
+    ModelClass = apps.get_model(app_label, model_name)
+
+    # separate transaction for the expensive counting
+    with durable_atomic():
+        count = ModelClass.objects.count()
+
+    with immediate_atomic():
+        CachedModelCount.objects.update_or_create(
+            app_label=app_label,
+            model_name=model_name,
+            defaults={
+                'count': count,
+                'last_updated': timezone.now(),
+            },
+        )