Fix batch_fetch

sqlalchemy_utils/batch.py

@@ -14,8 +14,6 @@ from sqlalchemy_utils.functions.orm import (
     list_local_values,
     list_local_remote_exprs,
     local_values,
-    local_column_names,
-    local_remote_expr,
     remote_column_names,
     remote_values,
     remote
@@ -339,9 +337,10 @@ class GenericRelationshipFetcher(object):
         id_dict = defaultdict(list)
         for entity in self.path.entities:
             discriminator = getattr(entity, self.prop._discriminator_col.key)
-            id_dict[discriminator].append(
-                getattr(entity, self.prop._id_col.key)
-            )
+            for id_col in self.prop._id_cols:
+                id_dict[discriminator].append(
+                    getattr(entity, id_col.key)
+                )
         return chain(*self._queries(sa.inspect(entity), id_dict))
 
     def _queries(self, state, id_dict):

sqlalchemy_utils/functions/orm.py

@@ -77,7 +77,8 @@ def remote(prop):
 def local_column_names(prop):
     if not hasattr(prop, 'secondary'):
         yield prop._discriminator_col.key
-        yield prop._id_col.key
+        for id_col in prop._id_cols:
+            yield id_col.key
     elif prop.secondary is None:
         for local, _ in prop.local_remote_pairs:
             yield local.name