Quick dirty SQLAlchemy middleware for django < 1.9

sqlalchemy_middleware.py

from sqlalchemy.engine import create_engine
from sqlalchemy.orm import sessionmaker


def create_engine_from_django_settings(database='default'):
    from django.conf import settings
    db = settings.DATABASES[database]
    engine = db['ENGINE'].lower()
    if 'postgresql' in engine:
        sqlalchemy_engine = 'postgresql'
    elif 'mysql' in engine:
        sqlalchemy_engine = 'mysql'
    elif 'sqlite' in engine:
        sqlalchemy_engine = 'sqlite'
    else:
        raise NotImplementedError('Could not determine what engine to use for "%s" automatically' % engine)
    host = db['HOST']
    name = db['NAME']
    credentials = [db['USER']]
    password = db['PASSWORD']
    if password:
        credentials.append(password)

    user_password = ':'.join(credentials)

    dsn = '{engine}://{user_password}@{host}/{name}'.format(
        engine=sqlalchemy_engine, user_password=user_password, host=host, name=name)

    return create_engine(dsn)


class SqlAlchemySession:
    def __init__(self):
        self.Session = sessionmaker(bind=create_engine_from_django_settings('postgres_db'))

    def process_request(self, request):
        request.db_session = self.Session()
        return None

    def process_exception(self, request, exception):
        setattr(request, '_exception', exception)
        try:
            session = request.db_session
        except AttributeError:
            pass
        else:
            session.rollback()
        return None

    def process_response(self, request, response):
        try:
            session = request.db_session
        except AttributeError:
            return response
        else:
            if getattr(request, '_exception', None) is None:
                session.commit()
        session.close()
        return response