[Django]-Scoped_session(sessionmaker()) or plain sessionmaker() in sqlalchemy?

Scoped_session at every method will give you a thread of local session which you cannot obtain beforehand (like at the module level).It’s not needed to open a new session in every method, You can use a global session , Create a session only when the global session is not available. i.e you can write a method which returns a session and add it to the init.py inside your package.

Don’t use scoped_session and don’t use Flask-SQLAlchemy.

Just use Session = sessionmaker() held in a singleton/service class, and use session = Session() on every HTTP request to guarantee that a fresh connection is provided.

Thread Local storage is clumsy and involves holding state which doesn’t play nicely with different web-server threading models. Better to stay stateless. See for example SqlAlchemy’s documentation here mentioning not to forget to call .remove() if you are using scoped_session. Will anyone remember to do that?

Below is an excerpt from https://docs.sqlalchemy.org/en/14/orm/contextual.html#using-thread-local-scope-with-web-applications:

Using the above flow, the process of integrating the Session with the web application has exactly two requirements:

• Create a single scoped_session registry when the web application first starts, ensuring that this object is accessible by the rest of the application.

• Ensure that scoped_session.remove() is called when the web request ends, usually by integrating with the web framework’s event system to establish an “on request end” event.

FYI, when using flask-sqlalchemy, the session object provided is by default a scoped session object.

http://flask-sqlalchemy.pocoo.org/2.3/quickstart/#road-to-enlightenment

I am looking into this myself, but I am not an expert.

My three points are:

1. SQLAlchemy docs provide a proposed approach using scoped_session, per Mr. Kluev’s comment above, at this link: http://docs.sqlalchemy.org/en/rel_0_9/orm/session.html#using-thread-local-scope-with-web-applications.
2. At that web location, the SQLAlchemy docs also say that it is “…strongly recommended that the integration tools provided with the web framework itself be used, if available, instead of scoped_session.”
3. Flask-SQLAlchemy, for example, appears to claim that it takes care of this: http://pythonhosted.org/Flask-SQLAlchemy/quickstart.html#a-minimal-application