usually some kind of collection of objects you want to keep is maintained, it
can be passed throughout those methods, or it can be attached to the Session.
It's a tradeoff between which objects you'd like to keep around between calls
to things, and which you'd like to be garbage collected.
On May 22, 2013, at 3:49 AM, Etienne Rouxel <rouxel.etie...@gmail.com> wrote:
> My real application seems to share the cause for why the identity map is not
> used. Indeed, I have a method that encapsulate the building of a form using
> queries. Once the execution goes out of this method, the instances are
> cleared out from the identity map.
> I guess this is a very common concern, is there any appropriate design
> pattern to fully take advantage of the identity map?
>
> Le mardi 21 mai 2013 17:31:10 UTC+2, Etienne Rouxel a écrit :
> Hello
> In my program, I was trying to guess why so many SQL queries were sent while
> some could have been avoided with the help of the identity map.
> So, I reduced my program to what is below and wrote 3 times the same
> query.get call and 3 SQL queries were sent to the database server.
> Why does SQLAlchemy send 3 times the SQL while it could have done it only 1
> time for the first call and use the identity map for the 2 last calls?
>
> from sqlalchemy import *
> from sqlalchemy.orm import *
> from sqlalchemy.ext.declarative import declarative_base
> Base = declarative_base()
>
> _descriptiontype_table = Table('descriptiontype', Base.metadata,
> Column('id', Integer, primary_key=True),
> Column('refno', Integer),
> Column('sortindex', Integer),
> Column('designation', String),
> schema='botany'
> )
>
> class Descriptiontype(Base):
> __table__ = _descriptiontype_table
>
> if __name__ == '__main__':
>
> engine = create_engine('postgresql://user@localhost:5432/mydatabase')
> Session = sessionmaker(bind=engine)
> session = Session()
>
> session.query(Descriptiontype).get(-2147483648)
> session.query(Descriptiontype).get(-2147483648)
> session.query(Descriptiontype).get(-2147483648)
>
>
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