Discussion on: Python: a workaround for SQLAlchemy “Table 'sessions' is already defined” exception during tests.

[Lex]

Ok I may decide to add again the "keep_existing": True, however this shouldn't be needed. If you delete or comment the following lines and use 0.8.0, I would be interested to know the result. There should be no need to manually create the table as flask-session does this now.

# try:
   # from book_keeping.library.fixed_session import FixedSession as Session
# except ImportError:
    # print( 'from flask_session import Session' )
from flask_session import Session

and

with app.app_context():

   # app_session.app.session_interface.client.create_all()

[Be Hai Nguyen]

Hi Lex,

Based on your advice:

E:\book-keeping\src\book_keeping\__init__.py modified to:

"""
Application package.
"""
from flask import Flask
from flask_sqlalchemy import SQLAlchemy

from flask_session import Session

...
def init_app_session( app ):
    app.config[ 'SESSION_SQLALCHEMY' ] = db

    # app_session = Session( app )
    # with app.app_context():
    #    app_session.app.session_interface.client.create_all()
... 

I have also decided to use latest of everything, E:\book-keeping\setup.py updated to:

...
    install_requires=[
        'Flask',
        'python-dotenv',
        'mysql-connector-python',
        'Flask-Login',
        'Flask-SQLAlchemy',
        'Flask-Session',
        'Flask-Bcrypt',
        'Flask-WTF',
        'PyYAML',
        'simplejson',
        'email-validator',
        'xhtml2pdf',
        'blinker',
        'pytest',
        'coverage',
    ],
... 

I am using the original Flask-Session 0.8.0:

Test 1: table sessions exists:

• The application runs. That is, venv\Scripts\flask.exe run does not raise exception.

• Tests no longer raise the table sessions exists exception. They now raise another unrelated exception.

Test 2: I manually removed the existing sessions table:

The results are as in Test 1. BUT THE TABLE sessions DOES NOT GET CREATED.

Further note:

With:

def init_app_session( app ):
    app.config[ 'SESSION_SQLALCHEMY' ] = db

    app_session = Session( app )
    with app.app_context():
        app_session.app.session_interface.client.create_all()

• Tests raise the old exception (0.4.0). But the sessions table gets created.

• venv\Scripts\flask.exe run no longer raises the old exception (0.4.0) and the table sessions table also gets created.

Please note that, I posted this article on the 24th, November 2022. And labelled the code for this article. That is why I am able to get the code test this problem. I forgot to label database version!

Since the this article, I added more functionalities including database changes till around May 2023, I have since stopped working on this project.

For these tests, for the application (that is, venv\Scripts\flask.exe run), I can only get to the login page. But that should be enough.

Please let me know if you want me to do anything else.

Thank you and best regards,

...behai.

[Be Hai Nguyen]

Hi @lxstr,

Your advice works.

And this report from my last response is not correct:

Test 2: I manually removed the existing sessions table:

The results are as in Test 1. BUT THE TABLE sessions DOES NOT GET CREATED.

There was something in my code what caused it not to work. I am using all latest packages now.

There is no need for:

Ok I may decide to add again the "keep_existing": True

dev.to/lxstr/comment/2e7gb

I do apologise for all the fault alarms. I appreciate your helps.

Thank you and best regards,

...behai.

P.S.

Just a side note, my application has a view session functionality for admins, whereby it just displays existing sessions as JSON. I was using pickle to serialise the session data. Flask-Session 0.8.0 now uses msgspec, the serialisation of sessions.data is now:

data = msgspec.msgpack.Decoder().decode(<value of sessions.data>)