SQLAlchemy, get object not bound to a Session

In my case, I was saving a related entity as well, and this recipe helped me to refresh all instances within a session, leveraging the fact that Session is iterable:

map(session.refresh, iter(session))  # call refresh() on every instance

This is extremely ineffective, but works. Should be fine for unit-tests.

Final note: in Python3 map() is a generator and won't do anything. Use real loops of list comprehensions

This often happens due to objects being in expired state, objects get expired for example after committing, then when such expired objects are about to get used the ORM tries to refresh them, but this cannot be done when objects are detached from session (e.g. because that session was closed). This behavior can be managed by creating session with expire_on_commit=False param.

>>> from sqlalchemy import inspect
>>> insp = inspect(my_object)
>>> insp.expired
True  # then it will be refreshed...

If you want a bunch of objects produced by querying a session to be usable outside the scope of the session, you need to expunge them for the session.

In your first function example, you will need to add a line:

session.expunge_all()

before

session.close()

More generally, let's say the session is not closed right away, like in the first example. Perhaps this is a session that is kept active during entire duration of a web request or something like that. In such cases, you don't want to do expunge_all. You will want to be more surgical:

for item in lst:
    session.expunge(item)