Fix db_migrate.py show error and back trace while loading configuration on Linecard (#3257)

Fix db_migrate.py show error and back trace while loading configuration on Linecard

#### Why I did it
    Fix [issue @](#18389)

#### How I did it
    Revert code change by sonic-net/sonic-utilities#3100
    Check DB config initialize state and ignore when initialized.

#### How to verify it
    Pass all UT.
    Manually test.

##### Work item tracking
- Microsoft ADO **(number only)**: 27384235

#### Which release branch to backport (provide reason below if selected)
    N/A

#### Description for the changelog
    Fix db_migrate.py show error and back trace while loading configuration on Linecard

#### A picture of a cute animal (not mandatory but encouraged)

Author: liuh-80

scripts/db_migrator.py

@@ -8,10 +8,9 @@
 import re
 
 from sonic_py_common import device_info, logger
-from swsscommon.swsscommon import SonicV2Connector, ConfigDBConnector
+from swsscommon.swsscommon import SonicV2Connector, ConfigDBConnector, SonicDBConfig
 from minigraph import parse_xml
 from utilities_common.helper import update_config
-from utilities_common.general import load_db_config
 
 INIT_CFG_FILE = '/etc/sonic/init_cfg.json'
 MINIGRAPH_FILE = '/etc/sonic/minigraph.xml'
@@ -1277,7 +1276,14 @@ def main():
         socket_path = args.socket
         namespace = args.namespace
 
-        load_db_config()
+        # Can't load global config base on the result of is_multi_asic(), because on multi-asic device, when db_migrate.py
+        # run on the local database, ASIC instance will have not created the /var/run/redis0/sonic-db/database-config.json
+        if args.namespace is not None:
+            if not SonicDBConfig.isGlobalInit():
+                SonicDBConfig.initializeGlobalConfig()
+        else:
+            if not SonicDBConfig.isInit():
+                SonicDBConfig.initialize()
 
         if socket_path:
             dbmgtr = DBMigrator(namespace, socket=socket_path)

tests/db_migrator_test.py

@@ -5,7 +5,7 @@
 from unittest import mock
 from deepdiff import DeepDiff
 
-from swsscommon.swsscommon import SonicV2Connector
+from swsscommon.swsscommon import SonicV2Connector, SonicDBConfig
 from sonic_py_common import device_info
 
 from .mock_tables import dbconnector
@@ -889,6 +889,22 @@ def test_init(self, mock_args):
         import db_migrator
         db_migrator.main()
 
+    @mock.patch('argparse.ArgumentParser.parse_args')
+    @mock.patch('swsscommon.swsscommon.SonicDBConfig.isInit', mock.MagicMock(return_value=False))
+    @mock.patch('swsscommon.swsscommon.SonicDBConfig.initialize', mock.MagicMock())
+    def test_init_no_namespace(self, mock_args):
+        mock_args.return_value=argparse.Namespace(namespace=None, operation='version_202405_01', socket=None)
+        import db_migrator
+        db_migrator.main()
+
+    @mock.patch('argparse.ArgumentParser.parse_args')
+    @mock.patch('swsscommon.swsscommon.SonicDBConfig.isGlobalInit', mock.MagicMock(return_value=False))
+    @mock.patch('swsscommon.swsscommon.SonicDBConfig.initializeGlobalConfig', mock.MagicMock())
+    def test_init_namespace(self, mock_args):
+        mock_args.return_value=argparse.Namespace(namespace="asic0", operation='version_202405_01', socket=None)
+        import db_migrator
+        db_migrator.main()
+
 
 class TestGNMIMigrator(object):
     @classmethod