Strange "objectdeletederror" when transferring instance between transactional sessions

[Former user]

On SQLAlchemy-0.5.7-py2.6.egg, with MYSQL databases (sqllite has no problems): - I begin two transactional sessions (no autocommit) - I create and commit an instance via the first one - I close the first session (the instance is now detached) - I add the instance to the second session

Then the instance is actually NOT properly added to the second session, trying to access its attributes raises misc. errors like "objectdeteletederror" or "not in persistent state".

Note that the problem doesn't apear if I only create the second session after closing the first one, or if I don't "initialize" its transaction by issuing a query on it before adding the instance.

[Former user]

reproduces the "broken adding of instance to session" with mysql

[Mike Bayer]

this is a simple effect of transaction isolation. MySQL's docs on this are here:

http://dev.mysql.com/doc/refman/5.1/en/innodb-transaction-model.html

basically Session2 has already begun a transaction and has read all rows of the table. Changes to this table will not be visible until it begins a new transaction. You can see the effect as follows:

session2.rollback()

# transfer to session 2
session2.add(a)

# works !
print a.ssi_acronym

[Former user]

Allright, I hadn't noticed that "transient" and "detached" instances were so different... actually a transient instance is like a normal python object, containing its full information, whereas a detached object is like a pointer to DB fields, needing a functional session to retrieve its attributes...

I guess I get it now, thanks.