Initial support for many-to-many relationship batch fetching

CHANGES.rst

@@ -4,6 +4,12 @@ Changelog
 Here you can see the full list of changes between each SQLAlchemy-Utils release.
 
 
+0.16.4 (2013-08-08)
+^^^^^^^^^^^^^^^^^^^
+
+- Initial many-to-many relations support for batch_fetch
+
+
 0.16.3 (2013-08-05)
 ^^^^^^^^^^^^^^^^^^^
 

setup.py

@@ -55,7 +55,7 @@ for name, requirements in extras_require.items():
 
 setup(
     name='SQLAlchemy-Utils',
-    version='0.16.3',
+    version='0.16.4',
     url='https://github.com/kvesteri/sqlalchemy-utils',
     license='BSD',
     author='Konsta Vesterinen',

sqlalchemy_utils/__init__.py

@@ -34,7 +34,7 @@ from .types import (
 )
 
 
-__version__ = '0.16.3'
+__version__ = '0.16.4'
 
 
 __all__ = (

sqlalchemy_utils/functions.py

@@ -390,7 +390,7 @@ def render_statement(statement, bind=None):
     return Compiler(bind.dialect, statement).process(statement)
 
 
-def batch_fetch(entities, attr):
+def batch_fetch(entities, *attr_paths):
     """
     Batch fetch given relationship attribute for collection of entities.
 
@@ -412,41 +412,94 @@ def batch_fetch(entities, attr):
 
         batch_fetch(users, User.phonenumbers)
     """
+
     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])
+        for attr_path in attr_paths:
+            if isinstance(attr_path, six.string_types):
+                attrs = attr_path.split('.')
+
+                if len(attrs) > 1:
+                    related_entities = []
+                    for entity in entities:
+                        related_entities.extend(getattr(entity, attrs[0]))
+
+                    batch_fetch(related_entities, '.'.join(attrs[1:]))
+                    continue
+                else:
+                    attr = getattr(
+                        first.__class__, attrs[0]
+                    )
+            else:
+                attr = attr_path
+
+            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 prop.secondary is None:
+                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
+
+                related_entities = (
+                    session.query(model)
+                    .filter(
+                        getattr(model, column_name).in_(parent_ids)
+                    )
+                )
+
+                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]
+                    )
+            else:
+                column_name = None
+                for column in prop.remote_side:
+                    for fk in column.foreign_keys:
+                        # TODO: make this support inherited tables
+                        if fk.column.table == first.__class__.__table__:
+                            column_name = fk.parent.name
+                            break
+                    if column_name:
+                        break
+
+                related_entities = (
+                    session
+                    .query(model, getattr(prop.secondary.c, column_name))
+                    .join(
+                        prop.secondary, prop.secondaryjoin
+                    )
+                    .filter(
+                        getattr(prop.secondary.c, column_name).in_(
+                            parent_ids
+                        )
+                    )
+                )
+                for entity, parent_id in related_entities:
+                    parent_dict[parent_id].append(
+                        entity
+                    )
+
+                for entity in entities:
+                    set_committed_value(
+                        entity, prop.key, parent_dict[entity.id]
+                    )

tests/__init__.py

@@ -28,6 +28,7 @@ class TestCase(object):
 
     def setup_method(self, method):
         self.engine = create_engine(self.dns)
+        #self.engine.echo = True
         self.connection = self.engine.connect()
         self.Base = declarative_base()
 

tests/test_batch_fetch.py

@@ -1,22 +1,91 @@
+import sqlalchemy as sa
 from pytest import raises
 from sqlalchemy_utils import batch_fetch
 from tests import TestCase
 
 
 class TestBatchFetch(TestCase):
+    def create_models(self):
+        class User(self.Base):
+            __tablename__ = 'user'
+            id = sa.Column(sa.Integer, autoincrement=True, primary_key=True)
+            name = sa.Column(sa.Unicode(255))
+
+        class Category(self.Base):
+            __tablename__ = 'category'
+            id = sa.Column(sa.Integer, primary_key=True)
+            name = sa.Column(sa.Unicode(255))
+
+        class Article(self.Base):
+            __tablename__ = 'article'
+            id = sa.Column(sa.Integer, primary_key=True)
+            name = sa.Column(sa.Unicode(255))
+            category_id = sa.Column(sa.Integer, sa.ForeignKey(Category.id))
+
+            category = sa.orm.relationship(
+                Category,
+                primaryjoin=category_id == Category.id,
+                backref=sa.orm.backref(
+                    'articles'
+                )
+            )
+
+        article_tag = sa.Table(
+            'article_tag',
+            self.Base.metadata,
+            sa.Column(
+                'article_id',
+                sa.Integer,
+                sa.ForeignKey('article.id', ondelete='cascade')
+            ),
+            sa.Column(
+                'tag_id',
+                sa.Integer,
+                sa.ForeignKey('tag.id', ondelete='cascade')
+            )
+        )
+
+        class Tag(self.Base):
+            __tablename__ = 'tag'
+            id = sa.Column(sa.Integer, primary_key=True)
+            name = sa.Column(sa.Unicode(255))
+            articles = sa.orm.relationship(
+                Article,
+                secondary=article_tag,
+                backref=sa.orm.backref(
+                    'tags'
+                )
+            )
+
+        self.User = User
+        self.Category = Category
+        self.Article = Article
+        self.Tag = Tag
+
     def setup_method(self, method):
         TestCase.setup_method(self, method)
-        category = self.Category(name=u'Category #1')
-        category.articles = [
+        articles = [
             self.Article(name=u'Article 1'),
-            self.Article(name=u'Article 2')
-        ]
-        category2 = self.Category(name=u'Category #2')
-        category2.articles = [
+            self.Article(name=u'Article 2'),
             self.Article(name=u'Article 3'),
             self.Article(name=u'Article 4'),
             self.Article(name=u'Article 5')
         ]
+        self.session.add_all(articles)
+        self.session.flush()
+
+        tags = [
+            self.Tag(name=u'Tag 1'),
+            self.Tag(name=u'Tag 2'),
+            self.Tag(name=u'Tag 3')
+        ]
+        articles[0].tags = tags
+        articles[3].tags = tags[1:]
+
+        category = self.Category(name=u'Category #1')
+        category.articles = articles[0:2]
+        category2 = self.Category(name=u'Category #2')
+        category2.articles = articles[2:]
         self.session.add(category)
         self.session.add(category2)
         self.session.commit()
@@ -32,3 +101,14 @@ class TestBatchFetch(TestCase):
         query_count = self.connection.query_count
         categories[0].articles  # no lazy load should occur
         assert self.connection.query_count == query_count
+
+    def test_multiple_relationships(self):
+        categories = self.session.query(self.Category).all()
+        batch_fetch(
+            categories,
+            'articles',
+            'articles.tags'
+        )
+        query_count = self.connection.query_count
+        categories[0].articles[0].tags
+        assert self.connection.query_count == query_count