Integrate SQLAlchemy with Falcon framework

To integrate SQLAlchemy with Falcon framework we can use middleware component. I will show you how to create a simple middleware which will create a session for every request and roll back changes if something fails.

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)

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'):
            if not req_succeeded:
                resource.session.rollback()
            Session.remove()

import falcon


app = falcon.API(middleware=[
    SQLAlchemySessionManager(Session),
])

Session is accessible for 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()