On 08/24/2016 03:09 PM, Gordan Todorovac wrote:
Mike,
python -i ~/python/sq3.py
from sqlalchemy import create_engine
from sqlalchemy.orm import Session
e = create_engine("sqlite:///:memory:")
Base.metadata.drop_all(e)
Base.metadata.create_all(e)
session=Session(e)
rory=User("rory")
session.add(rory)
chicken=Keyword("chicken")
session.add(chicken)
rory.keywords.append(chicken)
rory.keywords
[Keyword('chicken')]
chicken.users
[<__main__.User object at 0x7f82dff87390>]
Here, nothing is flushed yet. UserKeyword is a pending object and has
not been inserted.
rory.keywords.remove(chicken)
Here, you've removed from User.user_keywords, marked the UserKeyword as
deleted, and since it was never inserted, it's bumped out of the
session.
rory.keywords
[]
rory.user_keywords is empty.
chicken.users
[None]
chicken.user_keywords still has the UserKeyword object stuck in it, the
UserKeyword has no User attached to it, so the user name is None.
There is no relationship between UserKeyword.keyword and
UserKeyword.user, so you'd need to wait for the session to be expired
and have this totally unrelated relationship load again, or perhaps use
attribute events of your own to synchronize these ahead of re-loading.
session.flush()
/hostname/multiacl2/lib/python2.7/site-packages/sqlalchemy/orm/unitofwork.py:235:
SAWarning: Object of type <UserKeyword> not in session, add operation
along 'Keyword.user_keywords' will not proceed
this warning is because this is an odd situation where you've added a
UserKeyword as pending, never flushed it, and have now removed it from
the session, but it's still sitting inside of a collection.
chicken.user_keywords
[<__main__.UserKeyword object at 0x7f82dfa6ded0>]
expected, same reasons above
chicken.user_keywords[0].user
chicken.user_keywords[0].keyword
Keyword('chicken')
expected, same reason above.
type "session.commit()". Now everything is what you'd expect.
This is also explained in my answer at
http://stackoverflow.com/a/14471166/34549.
The bug explained in that answer is that prior to 0.8, the UserKeyword
object in question *would still be in the Session*, and since it's
"user" is None, you get a NULL error - the original poster reported:
"Causes an integrity error as SA tries to set one of the foreign key
columns to null.". That's the part that was fixed.
So it definitely seems that the association object is
half-disassociated. I have this currently worked around by setting a
validator on UserKeyword.user that removes self from
UserKeyword.keyword.user_keywords if self.user is None, but I am not
confident in this workaround.
On Wednesday, August 24, 2016 at 1:57:58 PM UTC-4, Mike Bayer wrote:
The issue mentioned in 2655 is a major behavior of the ORM, in that an
object is considered orphan if any of its relationships are non-present
in all cases, including pending and persistent, rather than if all of
them are un-present. This is not at all subtle and is covered in a
wide range of test cases. The test case attached to the bug continues
to pass, as does the demonstration attached in the migration notes:
http://docs.sqlalchemy.org/en/latest/changelog/migration_08.html#the-consideration-of-a-pending-object-as-an-orphan-has-been-made-more-aggressive
<http://docs.sqlalchemy.org/en/latest/changelog/migration_08.html#the-consideration-of-a-pending-object-as-an-orphan-has-been-made-more-aggressive>.
>
>
> Is anyone aware whether this bug was reintroduced on purpose (i.e.
> figured out the rationale for the original behavior) or by accident?
reintroduction of a bug here would need to be demonstrated.
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