fix(detectors): Ensure metric Detector deletion cleans up the AlertRule (#112425)

We don't really dual-write both ways, but we don't want to leave behind
the AlertRule when we delete a metric Detector.


Fixes ISWF-2389.

Author: kcons

src/sentry/deletions/defaults/detector.py

@@ -10,10 +10,29 @@ class DetectorDeletionTask(ModelDeletionTask[Detector]):
     manager_name = "objects_for_deletion"
 
     def get_child_relations(self, instance: Detector) -> list[BaseRelation]:
-        from sentry.workflow_engine.models import DataConditionGroup, DataSource
+        from sentry.incidents.models.alert_rule import AlertRule
+        from sentry.workflow_engine.models import (
+            AlertRuleDetector,
+            DataConditionGroup,
+            DataSource,
+        )
 
         model_relations: list[BaseRelation] = []
 
+        # If this detector was dual-written from an AlertRule, cascade deletion
+        # to the AlertRule. AlertRuleDeletionTask will handle cleaning up
+        # AlertRuleDetector, AlertRuleWorkflow, triggers, and incidents.
+        # NOTE: AlertRule must be deleted before DataSource so that
+        # QuerySubscriptionDeletionTask sees no remaining AlertRule referencing
+        # the SnubaQuery and can safely delete it.
+        alert_rule_ids = list(
+            AlertRuleDetector.objects.filter(detector_id=instance.id).values_list(
+                "alert_rule_id", flat=True
+            )
+        )
+        if alert_rule_ids:
+            model_relations.append(ModelRelation(AlertRule, {"id__in": alert_rule_ids}))
+
         # check that no other rows are related to the data source
         data_source_ids = DataSource.objects.filter(detector=instance.id).values_list(
             "id", flat=True

tests/sentry/deletions/test_detector.py

@@ -5,10 +5,14 @@
 from sentry.constants import ObjectStatus
 from sentry.deletions.tasks.scheduled import reattempt_deletions, run_scheduled_deletions
 from sentry.incidents.grouptype import MetricIssue
+from sentry.incidents.models.alert_rule import AlertRule, AlertRuleTrigger
 from sentry.snuba.models import QuerySubscription, SnubaQuery
 from sentry.testutils.hybrid_cloud import HybridCloudTestMixin
 from sentry.uptime.models import UptimeSubscription, get_uptime_subscription
+from sentry.workflow_engine.migration_helpers.alert_rule import dual_write_alert_rule
 from sentry.workflow_engine.models import (
+    AlertRuleDetector,
+    AlertRuleWorkflow,
     DataCondition,
     DataConditionGroup,
     DataSource,
@@ -262,3 +266,34 @@ def test_delete_uptime_subscription_without_detector(self) -> None:
             run_scheduled_deletions()
 
         assert not UptimeSubscription.objects.filter(id=uptime_sub_id).exists()
+
+
+class DeleteDualWrittenDetectorTest(BaseWorkflowTest, HybridCloudTestMixin):
+    def test_deleting_detector_deletes_associated_alert_rule(self) -> None:
+        alert_rule = self.create_alert_rule(
+            organization=self.organization,
+            projects=[self.project],
+        )
+        trigger = self.create_alert_rule_trigger(alert_rule=alert_rule)
+        dual_write_alert_rule(alert_rule)
+
+        snuba_query = alert_rule.snuba_query
+        subscription = QuerySubscription.objects.get(snuba_query=snuba_query)
+        detector = AlertRuleDetector.objects.get(alert_rule_id=alert_rule.id).detector
+        data_source = DataSource.objects.get(source_id=str(subscription.id))
+
+        detector.status = ObjectStatus.PENDING_DELETION
+        detector.save()
+        self.ScheduledDeletion.schedule(instance=detector, days=0)
+
+        with self.tasks():
+            run_scheduled_deletions()
+
+        assert not Detector.objects.filter(id=detector.id).exists()
+        assert not AlertRuleDetector.objects.filter(alert_rule_id=alert_rule.id).exists()
+        assert not AlertRuleWorkflow.objects.filter(alert_rule_id=alert_rule.id).exists()
+        assert not AlertRule.objects.filter(id=alert_rule.id).exists()
+        assert not AlertRuleTrigger.objects.filter(id=trigger.id).exists()
+        assert not DataSource.objects.filter(id=data_source.id).exists()
+        assert not QuerySubscription.objects.filter(id=subscription.id).exists()
+        assert not SnubaQuery.objects.filter(id=snuba_query.id).exists()

tests/sentry/workflow_engine/endpoints/test_organization_detector_index.py

@@ -9,9 +9,11 @@
 from sentry.deletions.tasks.scheduled import run_scheduled_deletions
 from sentry.grouping.grouptype import ErrorGroupType
 from sentry.incidents.grouptype import MetricIssue
+from sentry.incidents.models.alert_rule import AlertRule
 from sentry.models.environment import Environment
 from sentry.monitors.grouptype import MonitorIncidentType
 from sentry.search.utils import _HACKY_INVALID_USER
+from sentry.snuba.models import QuerySubscription, SnubaQuery
 from sentry.testutils.asserts import assert_org_audit_log_exists
 from sentry.testutils.cases import APITestCase
 from sentry.testutils.helpers.datetime import before_now
@@ -23,7 +25,12 @@
     DATA_SOURCE_UPTIME_SUBSCRIPTION,
 )
 from sentry.workflow_engine.endpoints.organization_detector_index import convert_assignee_values
-from sentry.workflow_engine.models import DataConditionGroup, Detector
+from sentry.workflow_engine.migration_helpers.alert_rule import dual_write_alert_rule
+from sentry.workflow_engine.models import (
+    AlertRuleDetector,
+    DataConditionGroup,
+    Detector,
+)
 from sentry.workflow_engine.models.detector_group import DetectorGroup
 from sentry.workflow_engine.typings.grouptype import IssueStreamGroupType
 
@@ -1369,3 +1376,30 @@ def test_delete_system_and_user_created_with_query_filters(self) -> None:
         )
 
         self.assert_unaffected_detectors([self.detector, error_detector])
+
+    def test_delete_dual_written_detector_cleans_up_alert_rule(self) -> None:
+        alert_rule = self.create_alert_rule(
+            organization=self.organization,
+            projects=[self.project],
+        )
+        self.create_alert_rule_trigger(alert_rule=alert_rule)
+        dual_write_alert_rule(alert_rule)
+
+        detector = AlertRuleDetector.objects.get(alert_rule_id=alert_rule.id).detector
+        snuba_query = alert_rule.snuba_query
+        subscription = QuerySubscription.objects.get(snuba_query=snuba_query)
+
+        with outbox_runner():
+            self.get_success_response(
+                self.organization.slug,
+                qs_params={"id": str(detector.id)},
+                status_code=204,
+            )
+
+        with self.tasks():
+            run_scheduled_deletions()
+
+        assert not Detector.objects.filter(id=detector.id).exists()
+        assert not AlertRule.objects.filter(id=alert_rule.id).exists()
+        assert not QuerySubscription.objects.filter(id=subscription.id).exists()
+        assert not SnubaQuery.objects.filter(id=snuba_query.id).exists()