First draft for batch_fetch

.travis.yml

@@ -8,6 +8,6 @@ python:
   - 2.7
   - 3.3
 install:
-  - pip install -q -e ".[test]" --use-mirrors
+  - pip install -e ".[test]"
 script:
   - python setup.py test

setup.py

@@ -33,7 +33,7 @@ extras_require = {
         'Jinja2>=2.3',
         'docutils>=0.10',
         'flexmock>=0.9.7',
-        'psycopg2>=2.4.6'
+        'psycopg2>=2.4.6',
     ],
     'arrow': ['arrow>=0.3.4'],
     'phone': [

sqlalchemy_utils/__init__.py

@@ -1,7 +1,12 @@
 from .exceptions import ImproperlyConfigured
 from .functions import (
-    sort_query, defer_except, escape_like, primary_keys, table_name,
-    render_statement
+    batch_fetch,
+    defer_except,
+    escape_like,
+    primary_keys,
+    render_statement,
+    sort_query,
+    table_name,
 )
 from .listeners import coercion_listener
 from .merge import merge, Merger
@@ -33,9 +38,8 @@ __version__ = '0.16.2'
 
 
 __all__ = (
-    ImproperlyConfigured,
+    batch_fetch,
     coercion_listener,
-    sort_query,
     defer_except,
     escape_like,
     instrumented_list,
@@ -43,10 +47,12 @@ __all__ = (
     primary_keys,
     proxy_dict,
     render_statement,
+    sort_query,
     table_name,
     ArrowType,
     ColorType,
     EmailType,
+    ImproperlyConfigured,
     InstrumentedList,
     IPAddressType,
     Merger,
@@ -59,8 +65,8 @@ __all__ = (
     PhoneNumber,
     PhoneNumberType,
     ProxyDict,
-    ScalarListType,
     ScalarListException,
+    ScalarListType,
     TimezoneType,
     TSVectorType,
     UUIDType,

sqlalchemy_utils/functions.py

@@ -386,3 +386,49 @@ def render_statement(statement, bind=None):
             return super(Compiler, self).render_literal_value(value, type_)
 
     return Compiler(bind.dialect, statement).process(statement)
+
+
+from sqlalchemy.orm.session import object_session
+from sqlalchemy.orm import RelationshipProperty
+from sqlalchemy.orm.attributes import set_committed_value
+
+
+def batch_fetch(entities, attr):
+    if entities:
+        first = entities[0]
+        if isinstance(attr, six.string_types):
+            attr = getattr(
+                first.__class__, attr
+            )
+
+        prop = attr.property
+        if not isinstance(prop, RelationshipProperty):
+            raise Exception(
+                'Given attribute is not a relationship property.'
+            )
+
+        model = prop.mapper.class_
+        session = object_session(first)
+
+        if len(prop.remote_side) > 1:
+            raise Exception(
+                'Only relationships with single remote side columns are '
+                'supported.'
+            )
+
+        column_name = list(prop.remote_side)[0].name
+        parent_ids = [entity.id for entity in entities]
+
+        related_entities = (
+            session.query(model)
+            .filter(
+                getattr(model, column_name).in_(parent_ids)
+            )
+        )
+
+        parent_dict = dict((entity.id, []) for entity in entities)
+        for entity in related_entities:
+            parent_dict[getattr(entity, column_name)].append(entity)
+
+        for entity in entities:
+            set_committed_value(entity, prop.key, parent_dict[entity.id])