Hello,
I have some SQLAlchemy-persisted instances of objects that have some
relationships coming from a parallel execution with multiprocessing. When I
reduce the results coming from the several processes, I need to merge some
relationships (`satellite` and `ground_station` objects in the code below)
since the associated object got another instance id during the
multiprocessing execution and if I don't merge I get an error like this:
sqlalchemy.exc.InvalidRequestError: Can't attach instance <Satellite>;
another instance with key <...> is already present in this session
Below the code responsible of this (where results is the reduced list
coming from the multiprocessing execution)
for passage in results:
# I need to merge since if coming from multiprocessing the instance
# IDs change.
passage.satellite = session.merge(passage.satellite)
passage.ground_station = session.merge(passage.ground_station)
session.add(passage)
This was working as expected when an attribute `satellite.tle` was
persisted in the database. I was asked now to remove that persistence from
the DB. So that attribute is present at runtime, but it's not in the
columns of the DB. `session.merge` now returns an objects where that `tle`
attribute is not present anymore.
So in the call:
passage.satellite = session.merge(passage.satellite)
the `satellite` object within `session.merge` correctly has the `tle` object,
while the returned object from `session.merge` does not. Is there a way to
avoid that merge strips off the attributes that are not persisted in the
database?
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