debugging DetachedInstanceError

[Jonathan Vanasco]

I'm trying to figure out how I got a DetatchedInstanceError

DetachedInstanceError: Parent instance <AcmeAuthorization at 0x107a62b90> is not bound to a Session; lazy load operation of attribute 'domain' cannot proceed (Background on this error at: http://sqlalche.me/e/bhk3)

This is happening in a web application where I never call `dbSession.close()`. It does use zope.sqlalchemy for pyramid_tm, but `keep_session` is True.  I set `expire_on_commit=False` on the sessionmaker.

Any tips on the best ways to troubleshoot how/where this is getting removed from a session?

[Mike Bayer]

Using the event hook is likely the most direct way to see where it's happening, either via logging or pdb:

https://docs.sqlalchemy.org/en/13/orm/events.html?highlight=persistent_to_detached#sqlalchemy.orm.events.SessionEvents.persistent_to_detached

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[Mike Bayer]

also the item can be detached if it was deleted in a previous flush

On Wed, Apr 22, 2020, at 8:57 PM, Jonathan Vanasco wrote:

[Jonathan Vanasco]

On Thursday, April 23, 2020 at 10:17:12 AM UTC-4, Mike Bayer wrote:

Using the event hook is likely the most direct way to see where it's happening, either via logging or pdb:

https://docs.sqlalchemy.org/en/13/orm/events.html?highlight=persistent_to_detached#sqlalchemy.orm.events.SessionEvents.persistent_to_detached

 

Awesome! Thanks mike. That's exactly what I needed.

After several hours of debugging, I finally tracked down the issue - which solved at least 4 outstanding bugs, and let me clear out a bunch of code.  And now I can have `expire_on_commit` back too!

I never realized that `zope.sqlalchemy.mark_changed(` has it's own `keep_session` kwarg... which defaults to `False` and does not inherit from the existing configuration. 

I can't tell why the errors on this was inconsistent.  The app has a simplified "commit" hook that lets me handle multiple `pyramid_tm` commits in a single request, and I invoke mark_changed() in there to pick up a few edge cases.  In a small number of these instances, I lost the `keep_session` setting - in others I didn't.