fix method

apps/establishment/models.py

@@ -2,7 +2,7 @@
 from datetime import datetime
 from functools import reduce
 from operator import or_
-from typing import List, Union
+from typing import List
 
 import elasticsearch_dsl
 from django.conf import settings
@@ -184,10 +184,9 @@ class EstablishmentQuerySet(models.QuerySet):
         """Return establishments by country code"""
         return self.filter(address__city__country=country)
 
-    def by_country_code(self, codes: Union[iter, str]):
+    def by_country_code(self, code: str):
         """Return establishments by country code"""
-        codes = codes if hasattr(codes, '__iter__') else [codes]
-        return self.filter(address__city__country__code__in=codes)
+        return self.filter(address__city__country__code=code)
 
     def published(self):
         """