chore(aci): update IssueAlertMigrator to handle existing AlertRuleDetector lookup case (#95295)

Author: cathteng

src/sentry/workflow_engine/migration_helpers/issue_alert_migration.py

@@ -131,15 +131,10 @@ def run(self) -> Workflow:
     def _create_detector_lookup(self) -> Detector:
 
         if self.is_dry_run:
-            created = True
             error_detector = Detector.objects.filter(
                 type=ErrorGroupType.slug, project=self.project
             ).first()
-            if error_detector:
-                created = not AlertRuleDetector.objects.filter(
-                    detector=error_detector, rule_id=self.rule.id
-                ).exists()
-            else:
+            if not error_detector:
                 error_detector = Detector(type=ErrorGroupType.slug, project=self.project)
 
         else:
@@ -148,12 +143,7 @@ def _create_detector_lookup(self) -> Detector:
                 project=self.project,
                 defaults={"config": {}, "name": ERROR_DETECTOR_NAME},
             )
-            _, created = AlertRuleDetector.objects.get_or_create(
-                detector=error_detector, rule_id=self.rule.id
-            )
-
-        if not created:
-            raise Exception("Issue alert already migrated")
+            AlertRuleDetector.objects.get_or_create(detector=error_detector, rule_id=self.rule.id)
 
         return error_detector
 
@@ -286,6 +276,8 @@ def _create_workflow_and_lookup(
             workflow = Workflow(**kwargs)
             workflow.full_clean(exclude=["when_condition_group"])
             workflow.validate_config(workflow.config_schema)
+            if AlertRuleWorkflow.objects.filter(rule_id=self.rule.id).exists():
+                raise Exception("Issue alert already migrated")
         else:
             workflow = Workflow.objects.create(**kwargs)
             workflow.update(date_added=self.rule.date_added)

tests/sentry/workflow_engine/migration_helpers/test_issue_alert_migration.py

@@ -327,6 +327,14 @@ def test_run__detector_exists(self):
         detector = Detector.objects.get(project_id=self.project.id)
         assert detector == project_detector
 
+    def test_run__detector_lookup_exists(self):
+        AlertRuleDetector.objects.create(
+            detector=self.create_detector(project=self.project),
+            rule_id=self.issue_alert.id,
+        )
+        IssueAlertMigrator(self.issue_alert, self.user.id).run()
+        AlertRuleWorkflow.objects.get(rule_id=self.issue_alert.id).workflow
+
     def test_run__with_conditions(self):
         issue_alert = self.create_project_rule(
             condition_data=self.conditions,