On Friday, February 15, 2013 7:36:22 AM UTC-7, Michael Bayer wrote:
> On Feb 14, 2013, at 5:18 PM, ru...@yahoo.com <javascript:> wrote:
> > What is the best way to get the .Person attribute updated to match
> > a new value assigned to .person?
> >
> > items = session.query(Task).order_by(Task.id).all()
> > print ('before change:\n', str(items[0].t2p_[0]), '\n Person =',
> str(items[0].t2p_[0].Person))
> > items[0].t2p_[0].person=21
> > print ('after change:\n', str(items[0].t2p_[0]), '\n Person =',
> str(items[0].t2p_[0].Person))
> > pass
>
> The ORM relationship construct is designed to work from the perspective of
> the object relationships being manipulated by the user, which then result
> in foreign key attributes being updated automatically. It does not
> automate the reverse direction, so while you are free to manipulate the
> value of integer foreign key attributes, the corresponding relationship
> attribute is only updated by loading the value from the database. So if
> you were to expire that attribute via Session.expire(Task, ['Person']) and
> then re-access it, new SQL would be emitted to reload this value, and
> assuming autoflush is enabled your change to the FK attribute will be
> flushed out and the SELECT will retrieve the new state. This expiration
> also happens automatically by default after a transaction is ended via
> commit().
>
> The best practices with SQLAlchemy though favor working with the object
> graph, that is task.Person = my_person, rather than dealing with FK
> attributes directly, since otherwise you're working against the automation
> features provided by relationship().
>
Thanks. Doing "...t2p_[0].Person = session.query(Person).get(21)" does
indeed change both
the .Person and the .person attributes in the T2P instance.
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