Dunno, let's try it:
import sqlalchemy as sa
import sqlalchemy.orm as saorm
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()
class Person(Base):
__tablename__ = 'people'
id = sa.Column(sa.Integer, primary_key=True, autoincrement=True)
name = sa.Column(sa.String(20))
if __name__ == '__main__':
engine = sa.create_engine('sqlite:///:memory:')
Base.metadata.create_all(engine)
Session = saorm.sessionmaker(bind=engine)
# Create our first session and use it to add a Person to the database
sess1 = Session()
sess1.add(Person(name='lars'))
sess1.commit()
sess1.close()
# Retrieve our Person from the database again.
person = sess1.query(Person).first()
# Now try to add that instance to a second session
sess2 = Session()
sess2.add(person)
sess2.commit()
Output:
Traceback (most recent call last):
...
sqlalchemy.exc.InvalidRequestError: Object '<Person at 0x10c9f5790>' is already
attached to session '1' (this is '2')
Looks very similar to your error message. I'm using SA 0.8.0 - it looks like
the message is slightly different in your version.
The correct thing to do in this case is to use "session.merge" to create a copy
of the object, attached to the new session. If you change the last few lines of
the script above to:
sess2 = Session()
merged = sess2.merge(person)
sess2.add(merged)
...it works fine.
Hope that helps,
Simon
On 2 Sep 2013, at 19:58, lars van Gemerden <l...@rational-it.com> wrote:
> Yes I know the question was a bit vague, but i couldn't think of a simple way
> to show some code. A test case would probably require some major surgery;
> I'll consider it though.
>
> It is possible that the second instance is associated with a different
> session, i'd have to check. What actually happens if you add the same
> instance to a second session?
>
> CL
>
>
> On Mon, Sep 2, 2013 at 8:23 PM, Simon King <si...@simonking.org.uk> wrote:
> Without knowing your application it's very difficult to know...
>
> Is there any chance that the second object is already associated with a
> different session? Perhaps from a different thread, or retrieved from a cache
> or something similar?
>
> Producing a standalone test script would help in diagnosing the problem.
>
> Simon
>
>
> On 2 Sep 2013, at 18:56, Lars van Gemerden <l...@rational-it.com> wrote:
>
> > Well, from the message yes, but i am not setting any primary keys manually,
> > so where could the second instance come from?
> >
> > CL
> >
> > ====================================
> > Lars van Gemerden
> > l...@rational-it.com
> > +31 6 26 88 55 39
> > ====================================
> >
> > On 2 sep. 2013, at 17:39, Simon King <si...@simonking.org.uk> wrote:
> >
> >> On Mon, Sep 2, 2013 at 4:01 PM, lars van gemerden <l...@rational-it.com>
> >> wrote:
> >>> Hi all,
> >>>
> >>> I have a one-to-one and many-to-one relationship (with an association
> >>> table
> >>> in the middle; Report.author-assoctable-Person.reports; why the table in
> >>> the
> >>> middle, you might ask, well it's a long story) and i am setting the author
> >>> on a specific Report twice to the same value. This gives the following
> >>> error:
> >>>
> >>> InvalidRequestError: Can't attach instance <person at 0x36a9350>;
> >>> another instance with key (<class 'models.data.classes.person'>, (2,)) is
> >>> already present in this session.
> >>>
> >>> The first time i set the author, it works and if i change the author it
> >>> works as well.
> >>>
> >>> This seems i little strange to me, why not be able to set the attribute to
> >>> the same value twice?
> >>>
> >>> Otherwise i have to check whether the new and old values are equal (which
> >>> through the peculiarties of my code is somewhat wastefull)
> >>>
> >>
> >> I think the message is actually telling you that you have 2 different
> >> instances of your "person" class with the same primary key. SQLAlchemy
> >> uses an identity map to ensure that a particular row in the database
> >> is only identified by a single instance within a particular session.
> >> If you violate that assumption (eg. by loading one instance of
> >> "person" from the database, then creating another instance and setting
> >> its primary key), you will get errors like this.
> >>
> >> Does that sound plausible?
> >>
> >> Simon
> >>
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> --
> ====================================
> Lars van Gemerden
> l...@rational-it.com
> +31 6 26 88 55 39
> ====================================
>
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