Added more tests and refactored batch fetch

sqlalchemy_utils/functions/batch_fetch.py

@@ -74,49 +74,17 @@ def batch_fetch(entities, *attr_paths):
     """
 
     if entities:
-        fetcher = BatchFetcher(entities)
+        fetcher = FetchingCoordinator(entities)
         for attr_path in attr_paths:
             fetcher(attr_path)
 
 
-class BatchFetcher(object):
+class FetchingCoordinator(object):
     def __init__(self, entities):
         self.entities = entities
         self.first = entities[0]
-        self.parent_ids = [entity.id for entity in entities]
         self.session = object_session(self.first)
 
-    def populate_backrefs(self, related_entities):
-        """
-        Populates backrefs for given related entities.
-        """
-
-        backref_dict = dict(
-            (entity.id, []) for entity, parent_id in related_entities
-        )
-        for entity, parent_id in related_entities:
-            backref_dict[entity.id].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]
-            )
-
-    def populate_entities(self):
-        """
-        Populate batch fetched entities to parent objects.
-        """
-        for entity in self.entities:
-            set_committed_value(
-                entity,
-                self.prop.key,
-                self.parent_dict[entity.id]
-            )
-
-        if self.should_populate_backrefs:
-            self.populate_backrefs(self.related_entities)
-
     def parse_attr_path(self, attr_path, should_populate_backrefs):
         if isinstance(attr_path, six.string_types):
             attrs = attr_path.split('.')
@@ -150,21 +118,97 @@ class BatchFetcher(object):
                 'are supported.'
             )
 
-        column_name = list(self.prop.remote_side)[0].name
-
-        self.related_entities = (
-            self.session.query(self.model)
-            .filter(
-                getattr(self.model, column_name).in_(self.parent_ids)
+    def fetcher(self, property_):
+        if not isinstance(property_, RelationshipProperty):
+            raise Exception(
+                'Given attribute is not a relationship property.'
             )
+
+        if property_.secondary is not None:
+            return ManyToManyFetcher(self, property_)
+        else:
+            if property_.direction.name == 'MANYTOONE':
+                return ManyToOneFetcher(self, property_)
+            else:
+                return OneToManyFetcher(self, property_)
+
+    def __call__(self, attr_path):
+        if isinstance(attr_path, with_backrefs):
+            self.should_populate_backrefs = True
+            attr_path = attr_path.attr_path
+        else:
+            self.should_populate_backrefs = False
+
+        attr = self.parse_attr_path(attr_path, self.should_populate_backrefs)
+        if not attr:
+            return
+
+        fetcher = self.fetcher(attr.property)
+        fetcher.fetch()
+        fetcher.populate()
+
+
+class Fetcher(object):
+    def __init__(self, coordinator, property_):
+        self.coordinator = coordinator
+        self.prop = property_
+        self.model = self.prop.mapper.class_
+        self.entities = coordinator.entities
+        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
+            )
+
+    @property
+    def local_values_list(self):
+        return [
+            self.local_values(entity)
+            for entity in self.entities
+        ]
+
+    def local_values(self, entity):
+        return getattr(entity, list(self.prop.local_columns)[0].name)
+
+    def populate_backrefs(self, related_entities):
+        """
+        Populates backrefs for given related entities.
+        """
+
+        backref_dict = dict(
+            (entity.id, []) for entity, parent_id in related_entities
         )
-
-        for entity in self.related_entities:
-            self.parent_dict[getattr(entity, column_name)].append(
-                entity
+        for entity, parent_id in related_entities:
+            backref_dict[entity.id].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]
             )
 
-    def fetch_association_entities(self):
+    def populate(self):
+        """
+        Populate batch fetched entities to parent objects.
+        """
+        for entity in self.entities:
+            set_committed_value(
+                entity,
+                self.prop.key,
+                self.parent_dict[self.local_values(entity)]
+            )
+
+        if self.coordinator.should_populate_backrefs:
+            self.populate_backrefs(self.related_entities)
+
+
+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:
@@ -183,7 +227,7 @@ class BatchFetcher(object):
             )
             .filter(
                 getattr(self.prop.secondary.c, column_name).in_(
-                    self.parent_ids
+                    parent_ids
                 )
             )
         )
@@ -192,30 +236,38 @@ class BatchFetcher(object):
                 entity
             )
 
-    def __call__(self, attr_path):
-        self.parent_dict = dict(
-            (entity.id, []) for entity in self.entities
+
+class ManyToOneFetcher(Fetcher):
+    def fetch(self):
+        column_name = list(self.prop.remote_side)[0].name
+
+        self.related_entities = (
+            self.session.query(self.model)
+            .filter(
+                getattr(self.model, column_name).in_(self.local_values_list)
+            )
         )
-        if isinstance(attr_path, with_backrefs):
-            self.should_populate_backrefs = True
-            attr_path = attr_path.attr_path
-        else:
-            self.should_populate_backrefs = False
 
-        attr = self.parse_attr_path(attr_path, self.should_populate_backrefs)
-        if not attr:
-            return
-
-        self.prop = attr.property
-        if not isinstance(self.prop, RelationshipProperty):
-            raise Exception(
-                'Given attribute is not a relationship property.'
+        for entity in self.related_entities:
+            self.parent_dict[getattr(entity, column_name)].append(
+                entity
             )
 
-        self.model = self.prop.mapper.class_
 
-        if self.prop.secondary is None:
-            self.fetch_relation_entities()
-        else:
-            self.fetch_association_entities()
-        self.populate_entities()
+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)
+            )
+        )
+
+        for entity in self.related_entities:
+            self.parent_dict[getattr(entity, column_name)].append(
+                entity
+            )

tests/batch_fetch/test_many_to_one_relationships.py

@@ -29,8 +29,16 @@ class TestBatchFetchManyToOneRelationships(TestCase):
     def setup_method(self, method):
         TestCase.setup_method(self, method)
         articles = [
-            self.Article(name=u'Article 1', author=self.User(name=u'John')),
-            self.Article(name=u'Article 2', author=self.User(name=u'Matt')),
+            self.Article(
+                id=1,
+                name=u'Article 1',
+                author=self.User(id=333, name=u'John')
+            ),
+            self.Article(
+                id=2,
+                name=u'Article 2',
+                author=self.User(id=334, name=u'Matt')
+            ),
         ]
         self.session.add_all(articles)
         self.session.commit()