migrations: Add migration to fix Attachment cache.

This migration needs to be run after the previous commit is deployed
to a given Zulip installation, to fix any stale values of
is_realm_public and is_web_public.

zerver/migrations/0386_fix_attachment_caches.py

@@ -0,0 +1,64 @@
+# Generated by Django 3.2.12 on 2022-03-23 04:32
+
+from django.db import migrations, models
+from django.db.backends.postgresql.schema import DatabaseSchemaEditor
+from django.db.migrations.state import StateApps
+from django.db.models import Exists, Model, OuterRef
+
+
+def fix_attachment_caches(apps: StateApps, schema_editor: DatabaseSchemaEditor) -> None:
+    Attachment = apps.get_model("zerver", "Attachment")
+    ArchivedAttachment = apps.get_model("zerver", "ArchivedAttachment")
+    Message = apps.get_model("zerver", "Message")
+    ArchivedMessage = apps.get_model("zerver", "ArchivedMessage")
+
+    BATCH_SIZE = 10000
+
+    def update_batch(attachment_model: Model, message_model: Model, lower_bound: int) -> None:
+        attachment_model.objects.filter(
+            id__gt=lower_bound, id__lte=lower_bound + BATCH_SIZE
+        ).update(
+            is_web_public=Exists(
+                message_model.objects.filter(
+                    attachment=OuterRef("id"),
+                    recipient__stream__invite_only=False,
+                    recipient__stream__is_web_public=True,
+                ),
+            ),
+            is_realm_public=Exists(
+                message_model.objects.filter(
+                    attachment=OuterRef("id"),
+                    recipient__stream__invite_only=False,
+                )
+            ),
+        )
+
+    max_id = Attachment.objects.aggregate(models.Max("id"))["id__max"]
+    if max_id is not None:
+        lower_bound = 0
+
+        while lower_bound < max_id:
+            print(f"Processed {lower_bound}/{max_id} attachments.")
+            update_batch(Attachment, Message, lower_bound)
+            lower_bound += BATCH_SIZE
+
+    max_id = ArchivedAttachment.objects.aggregate(models.Max("id"))["id__max"]
+    if max_id is not None:
+        lower_bound = 0
+
+        while lower_bound < max_id:
+            print(f"Processed {lower_bound}/{max_id} archived attachments.")
+            update_batch(ArchivedAttachment, ArchivedMessage, lower_bound)
+            lower_bound += BATCH_SIZE
+
+
+class Migration(migrations.Migration):
+    atomic = False
+
+    dependencies = [
+        ("zerver", "0385_attachment_flags_cache"),
+    ]
+
+    operations = [
+        migrations.RunPython(fix_attachment_caches, reverse_code=migrations.RunPython.noop),
+    ]