None! Can't pickle <class 'sqlalchemy.orm.session.Session'>: it's not the same object as sqlalchemy.orm.session.Session

[Haris Damara]

Hi,

Please help.

Find issue with error message "None! Can't pickle <class 'sqlalchemy.orm.session.Session'>: it's not the same object as sqlalchemy.orm.session.Session"

while run the sqlalchemy orm query and/or execute syntax in Process (multiprocessing)

[Simon King]

I haven't used the multiprocessing library, but if it uses pickle to
transfer SQLAlchemy objects, it's going to be difficult to make it
work. Objects loaded via the SQLAlchemy ORM hold a references to the
Session that was used to load them, which in turn holds a reference to
a database connection. Pickling the instance therefore tries to pickle
the Session as well, which almost certainly isn't what you want.

Rather than passing ORM instances to worker processes, it would
probably be better to either:

a) Pass a unique identifier for the instance, and have the worker
process reload the instance from the database itself, or
b) Send simpler (non-SQLAlchemy) objects to the worker,

Hope that helps,

Simon

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[Mike Bayer]

can confirm, don't try passing Session objects as arguments over multiprocessing.  that's not going to work for many reasons.   new child process should use its own session.

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