I'm having an issue where a list of user-defined objects is disappearing as
a function goes out of scope. The list is stored in a PickleType column,
and as that type does not track changes in the objects of the list, I am
(knowingly, inefficiently) forcing the column to become dirty by setting
the corresponding Python object to an empty list, and then to the new list
value. This is Python 2.7.3 with SQLAlchemy 0.9.8. The session I'm using
in the following code is created from a sessionmaker with default values
aside form *expire_on_commit*, which is False.
The declaration of the class containing the list is simplified to the
following:
class Target:
__tablename__ = 'targets'
id = Column(Integer, primary_key=True)
name = Column(Unicode)
targetList = Column(PickleType, default=[])
def run(dbSession):
targetInstance = makeTI(dbSession)#adds instance to session, flushes
modifyList(targetInstance, dbSession, data)#blinks list values, dirties
object in session. Flushes changes, and all list contents are still
subsequently present
assert not any(dbSession.dirty)#assert passes
assert not dbSession.is_modified(targetInstance)#assert passes
print 'targetInstance list contents after init: ' +
str(targetInstance.targetList)#prints list contents as expected
#last place list contents are present. Upon return of run(), list will
be empty again
return
After flow of control returns to the caller of run(), a commit is done,
then targetInstance is queried from the session, and the list is empty.
Even if the list is accessed, or explicitly refreshed from the session, the
list is empty. How is that possible if the once-dirty session was flushed?
I know that there is optional in-place mutation tracking, but that's not
being used here.
The relevant links are the official
<http://docs.sqlalchemy.org/en/rel_0_9/orm/extensions/mutable.html> mutable
docs, an extended conversation
<https://bitbucket.org/zzzeek/sqlalchemy/issue/2994/pickletype-gets-not-updated-in-database-in>
with Mike on BitBucket.
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