Since the id will only be available after a database insert; some flavor of
session.flush() is needed. I like to keep object constructors limited to
actual object construction; so putting it in get_person() after
instantiating the person seems best approach.
--
Mike Conley
On Mon, Jun 15, 2009 at 4:27 PM, JanW <jan.wu...@gmail.com> wrote:
>
> I am trying to access an objects primary key either in the constructor
> (preferred) or right after the object is created. And I would like to
> use a scoped session for this. Below is some dummy code to illustrate
> what I'm trying to do.
>
> I defined the get_person function to first query the database to see
> if the object already exists. If not it creates a new object.
>
> As is, the code will print 2 lines with in both cases 'None' as id.
>
> My question is, is there a way to make SA flush this object to the
> database as soon as possible? Making the session autoflush=True does
> not help.
>
> It does work if I enable the Session.object_session(self).flush() line
> in the constructor or in the get_person function, but this doesn't
> seem like a clean way to do it, especially not in the constructor. Is
> this the correct way to do it or does SA provide another, cleaner way?
> I would have expected autoflush to do this.
>
> (I can't do session.flush() since in reality session is not in the
> scope of either Person.__init__() or get_person(), they are both
> defined in my module's __init__.py while session is initialized in the
> script that imports the module.)
>
> Many thanks,
>
> Jan.
>
> ### demo code:
> ######
> from sqlalchemy import *
> from sqlalchemy.orm import *
>
> # Define SQLite databases
> person_engine = create_engine('sqlite:///person_db.sqlite')
>
> # Define database structure
> metadata=MetaData()
> metadata.bind = person_engine
>
> person_table = Table(
> 'person', metadata,
> Column('id', Integer, primary_key=True),
> Column('name', Text),
> )
>
> person_table.create()
>
> Session = scoped_session(sessionmaker())
> #Session = scoped_session(sessionmaker(autoflush=True))
> session = Session()
>
> class Person(object):
> def __init__(self, name):
> self.name = name
> # Session.object_session(self).flush()
> print "In constructor: id=%s"%self.id
>
> person_mapper = Session.mapper(Person, person_table)
>
> def get_person(name):
> result = Person.query().filter_by(name=name).first()
> if not result:
> result = Person(name)
> # Session.object_session(result).flush()
> print "New person made: id=%s, name=%s"%(result.id,
> result.name)
> return result
>
> p = get_person("Ed Jones")
>
> session.commit()
> session.close()
>
> >
>
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