SQLAlchemy and Falcon - session initialization

There is a package on pypi, falcon-sqla, that provides a middleware to manage SQLAlchemy sessions with Falcon.

It uses the request context object to add a different session to each http request, avoiding the need to use a scoped session.


You can use middleware

Example.

  1. Create engine, session_factory and scoped_session object.

    from sqlalchemy import create_engine
    from sqlalchemy.orm import scoped_session
    from sqlalchemy.orm import sessionmaker
    
    import settings
    
    
    engine = create_engine(
        '{engine}://{username}:{password}@{host}:{port}/{db_name}'.format(
        **settings.POSTGRESQL
        )
    )
    
    session_factory = sessionmaker(bind=engine)
    Session = scoped_session(session_factory)
    
  2. Create middleware.

    class SQLAlchemySessionManager:
        """
        Create a scoped session for every request and close it when the request
        ends.
        """
    
        def __init__(self, Session):
            self.Session = Session
    
        def process_resource(self, req, resp, resource, params):
            resource.session = self.Session()
    
        def process_response(self, req, resp, resource, req_succeeded):
            if hasattr(resource, 'session'):
                Session.remove()
    
  3. Register middleware.

    import falcon
    
    
    app = falcon.API(middleware=[
        SQLAlchemySessionManager(Session),
    ])
    
  4. Session is accessible in every request.

    import falcon
    
    
    class MyAPI:
    
        def on_get(self, req, resp):
            # You can access self.session here
            # self.session.add(foo)
            # self.session.commit()