@Charlie Clark:
In the documentation
(http://docs.sqlalchemy.org/en/rel_0_8/orm/session.html#session-frequently-asked-questions
see "Is the Session a cache ?"), it is mentioned that it does not
necessarily performs a query.
@Simon King:
I guess you're the King indeed, I tried:
1. to assign the result of the 3 queries to 3 different variables
2. to assign the result of the 3 queries to the same variable
3. to assign the result of the first query to a variable and not to assign
the result of the 2 last queries
In all these cases, only 1 SQL query were sent so your suspicion looks
correct.
Thank you both.
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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