Smarter local value checking for batch fetch

sqlalchemy_utils/functions/batch_fetch.py

@@ -157,11 +157,10 @@ class Fetcher(object):
         self.first = self.entities[0]
         self.session = object_session(self.first)
 
-        for entity in self.entities:
-            self.parent_dict = dict(
-                (self.local_values(entity), [])
-                for entity in self.entities
-            )
+        self.parent_dict = dict(
+            (self.local_values(entity), [])
+            for entity in self.entities
+        )
 
     @property
     def local_values_list(self):
@@ -177,17 +176,19 @@ class Fetcher(object):
         """
         Populates backrefs for given related entities.
         """
-
         backref_dict = dict(
-            (entity.id, []) for entity, parent_id in related_entities
+            (self.local_values(entity), [])
+            for entity, parent_id in related_entities
         )
         for entity, parent_id in related_entities:
-            backref_dict[entity.id].append(
+            backref_dict[self.local_values(entity)].append(
                 self.session.query(self.first.__class__).get(parent_id)
             )
         for entity, parent_id in related_entities:
             set_committed_value(
-                entity, self.prop.back_populates, backref_dict[entity.id]
+                entity,
+                self.prop.back_populates,
+                backref_dict[self.local_values(entity)]
             )
 
     def populate(self):
@@ -207,8 +208,6 @@ class Fetcher(object):
 
 class ManyToManyFetcher(Fetcher):
     def fetch(self):
-        parent_ids = [entity.id for entity in self.entities]
-
         column_name = None
         for column in self.prop.remote_side:
             for fk in column.foreign_keys:
@@ -227,7 +226,7 @@ class ManyToManyFetcher(Fetcher):
             )
             .filter(
                 getattr(self.prop.secondary.c, column_name).in_(
-                    parent_ids
+                    self.local_values_list
                 )
             )
         )
@@ -256,14 +255,12 @@ class ManyToOneFetcher(Fetcher):
 
 class OneToManyFetcher(Fetcher):
     def fetch(self):
-        parent_ids = [entity.id for entity in self.entities]
-
         column_name = list(self.prop.remote_side)[0].name
 
         self.related_entities = (
             self.session.query(self.model)
             .filter(
-                getattr(self.model, column_name).in_(parent_ids)
+                getattr(self.model, column_name).in_(self.local_values_list)
             )
         )