fix(api): make findings GIN index migration idempotent (#11129)

api/src/backend/api/migrations/0092_findings_arrays_gin_index_parent.py

@@ -7,8 +7,10 @@ PARENT_TABLE = "findings"
 
 def create_parent_and_attach(apps, schema_editor):
     with schema_editor.connection.cursor() as cursor:
+        # Idempotent: the parent index may already exist if it was created
+        # manually on an environment before this migration ran.
         cursor.execute(
-            f"CREATE INDEX {INDEX_NAME} ON ONLY {PARENT_TABLE} "
+            f"CREATE INDEX IF NOT EXISTS {INDEX_NAME} ON ONLY {PARENT_TABLE} "
             f"USING gin (categories, resource_services, resource_regions, resource_types)"
         )
         cursor.execute(
@@ -19,7 +21,20 @@ def create_parent_and_attach(apps, schema_editor):
         )
         for (partition,) in cursor.fetchall():
             child_idx = f"{partition.replace('.', '_')}_{INDEX_NAME}"
-            cursor.execute(f"ALTER INDEX {INDEX_NAME} ATTACH PARTITION {child_idx}")
+            # ALTER INDEX ... ATTACH PARTITION has no IF NOT ATTACHED clause,
+            # so check pg_inherits first to keep the migration re-runnable.
+            cursor.execute(
+                """
+                SELECT 1
+                FROM pg_inherits i
+                JOIN pg_class p ON p.oid = i.inhparent
+                JOIN pg_class c ON c.oid = i.inhrelid
+                WHERE p.relname = %s AND c.relname = %s
+                """,
+                [INDEX_NAME, child_idx],
+            )
+            if cursor.fetchone() is None:
+                cursor.execute(f"ALTER INDEX {INDEX_NAME} ATTACH PARTITION {child_idx}")
 
 
 def drop_parent_index(apps, schema_editor):