ref: remove unused attachment_id column part 1 (#82892)

blocked on #82891

<!-- Describe your PR here. -->

migrations_lockfile.txt

@@ -15,7 +15,7 @@ remote_subscriptions: 0003_drop_remote_subscription
 
 replays: 0004_index_together
 
-sentry: 0805_add_alert_and_member_invite_scopes_to_sentry_apps
+sentry: 0806_remove_monitor_attachment_id_pt1
 
 social_auth: 0002_default_auto_field
 

src/sentry/migrations/0806_remove_monitor_attachment_id_pt1.py

@@ -0,0 +1,33 @@
+# Generated by Django 5.1.4 on 2025-01-03 21:24
+
+from sentry.new_migrations.migrations import CheckedMigration
+from sentry.new_migrations.monkey.fields import SafeRemoveField
+from sentry.new_migrations.monkey.state import DeletionAction
+
+
+class Migration(CheckedMigration):
+    # This flag is used to mark that a migration shouldn't be automatically run in production.
+    # This should only be used for operations where it's safe to run the migration after your
+    # code has deployed. So this should not be used for most operations that alter the schema
+    # of a table.
+    # Here are some things that make sense to mark as post deployment:
+    # - Large data migrations. Typically we want these to be run manually so that they can be
+    #   monitored and not block the deploy for a long period of time while they run.
+    # - Adding indexes to large tables. Since this can take a long time, we'd generally prefer to
+    #   run this outside deployments so that we don't block them. Note that while adding an index
+    #   is a schema change, it's completely safe to run the operation after the code has deployed.
+    # Once deployed, run these manually via: https://develop.sentry.dev/database-migrations/#migration-deployment
+
+    is_post_deployment = False
+
+    dependencies = [
+        ("sentry", "0805_add_alert_and_member_invite_scopes_to_sentry_apps"),
+    ]
+
+    operations = [
+        SafeRemoveField(
+            model_name="monitorcheckin",
+            name="attachment_id",
+            deletion_action=DeletionAction.MOVE_TO_PENDING,
+        )
+    ]

src/sentry/monitors/models.py

@@ -12,7 +12,7 @@
 from django.conf import settings
 from django.db import models
 from django.db.models import Case, IntegerField, Q, Value, When
-from django.db.models.signals import post_delete, pre_save
+from django.db.models.signals import pre_save
 from django.dispatch import receiver
 from django.utils import timezone
 
@@ -533,8 +533,6 @@ class MonitorCheckIn(Model):
     that occurred during the check-in.
     """
 
-    attachment_id = BoundedBigIntegerField(null=True)
-
     objects: ClassVar[BaseManager[Self]] = BaseManager(cache_fields=("guid",))
 
     class Meta:
@@ -584,16 +582,6 @@ def _update_timestamps(self):
         pass
 
 
-def delete_file_for_monitorcheckin(instance: MonitorCheckIn, **kwargs):
-    if file_id := instance.attachment_id:
-        from sentry.models.files import File
-
-        File.objects.filter(id=file_id).delete()
-
-
-post_delete.connect(delete_file_for_monitorcheckin, sender=MonitorCheckIn)
-
-
 @region_silo_model
 class MonitorLocation(Model):
     __relocation_scope__ = RelocationScope.Excluded