KeyError / versioning_manager.units_of_work

[dfee]

I spent a good deal of time today working through this problem, and I figured I should document it here. The error becomes apparent when a user tries to flush objects that are versioned, but the session is not being tracked by the versioning_manager. A KeyError exception is raised as the session is not in versioning_manager.units_of_work.

make_versioned by default uses the default session factory for sqlalchemy (sqlalchemy.orm.session.Session). This behavior cannot be overridden either – versioning_manager.track_session(...) is called for whatever value is provided (i.e. None is not allowed, as an exception is thrown).

This is probably not a good idea, as common practices like dependency-injection break this. An example would be if a user is to generate his own session factory using sqlalchemy.orm.session.sessionmaker (as is encouraged).

Anyway, the solution here is to call versioning_manager.track_session(my_session_factory) with the my_session_factory the user has generated from sessionmaker.

[dalymople]

I also came across this issue when using SQLAlchemy-Continuum==1.3.6 with Flask, the FlaskPlugin and Flask-SQLAlchemy.

I found the best way around this was to pass the session factory at creation of the make_versioned class;
make_versioned(session=db.session, plugins=[FlaskPlugin()])

Maybe the docs the docs should be updated to state that you need to explicitly pass the session factory if you are not using the default factory?

[AbdealiLoKo]

This was happening due to the bug in sqlalchemy: sqlalchemy/sqlalchemy#8467
This ticket can be closed as sqlalchemt 1.4.41 is released which fixes this bug