Closes #22034: Fix rack group migration from very old netbox installation (#22063)

* #22034 fix rack group migation from very old netbox installation

* #22034 fix rack group migation from very old netbox installation

* #22034 fix rack group migation from very old netbox installation

* fix after loading old database

* simplify

* fix index name

netbox/dcim/migrations/0228_rack_group.py

@@ -14,6 +14,58 @@ class Migration(migrations.Migration):
     ]
 
     operations = [
+        # Rename legacy database objects left over from when the RackGroup model was renamed
+        # to Location (v2.11) and Rack.group was renamed to Rack.location. Old installations
+        # retained the original names, which conflict with the new dcim_rackgroup table and
+        # dcim_rack.group_id column created by this migration. No-op on fresh installs.
+        migrations.RunSQL(
+            sql=[
+                "ALTER INDEX IF EXISTS dcim_rackgroup_pkey RENAME TO dcim_location_pkey",
+                "ALTER INDEX IF EXISTS dcim_rackgroup_parent_id_cc315105 RENAME TO dcim_location_parent_id_d77f3318",
+                "ALTER INDEX IF EXISTS dcim_rackgroup_site_id_13520e89 RENAME TO dcim_location_site_id_b55e975f",
+                "ALTER INDEX IF EXISTS dcim_rackgroup_slug_3f4582a7 RENAME TO dcim_location_slug_352c5472",
+                "ALTER INDEX IF EXISTS dcim_rackgroup_slug_3f4582a7_like RENAME TO dcim_location_slug_352c5472_like",
+                "ALTER INDEX IF EXISTS dcim_rackgroup_tree_id_9c2ad6f4 RENAME TO dcim_location_tree_id_5089ef14",
+                "ALTER SEQUENCE IF EXISTS dcim_rackgroup_id_seq RENAME TO dcim_location_id_seq",
+                # Rename the legacy index on dcim_rack from when Rack.group was renamed to
+                # Rack.location. The column was renamed but the index was not, so it still
+                # carries the old "group_id" name while indexing location_id. Its name
+                # collides with the new index Django creates for the new Rack.group FK.
+                "ALTER INDEX IF EXISTS dcim_rack_group_id_44e90ea9 RENAME TO dcim_rack_location_id_5f63ec31",
+            ],
+            reverse_sql=migrations.RunSQL.noop,
+        ),
+        # PostgreSQL does not support IF EXISTS on RENAME CONSTRAINT, so use a DO block.
+        # Target names match what a fresh v4.5.9 install produces (Django generates the FK
+        # constraint name as <table>_<col>_<hash>_fk_<ref_table>_<ref_col>, where the hash is
+        # md5(table + col)[:8] computed against the new dcim_location table name).
+        migrations.RunSQL(
+            sql="""
+                DO $$
+                DECLARE
+                    r RECORD;
+                BEGIN
+                    FOR r IN (
+                        SELECT old_name, new_name FROM (VALUES
+                            ('dcim_rackgroup_level_check', 'dcim_location_level_check'),
+                            ('dcim_rackgroup_lft_check', 'dcim_location_lft_check'),
+                            ('dcim_rackgroup_rght_check', 'dcim_location_rght_check'),
+                            ('dcim_rackgroup_tree_id_check', 'dcim_location_tree_id_check'),
+                            ('dcim_rackgroup_site_id_13520e89_fk',
+                                'dcim_location_site_id_b55e975f_fk_dcim_site_id')
+                        ) AS m(old_name, new_name)
+                        WHERE EXISTS (
+                            SELECT 1 FROM pg_constraint
+                            WHERE conrelid = to_regclass('dcim_location') AND conname = m.old_name
+                        )
+                    ) LOOP
+                        EXECUTE format('ALTER TABLE dcim_location RENAME CONSTRAINT %I TO %I',
+                            r.old_name, r.new_name);
+                    END LOOP;
+                END $$;
+            """,
+            reverse_sql=migrations.RunSQL.noop,
+        ),
         migrations.CreateModel(
             name='RackGroup',
             fields=[