if an object is already attached to a session, you can get at that via object_session(instance). if the object is detached, itll return None.
if you want better ways to handle getting a session for objects that arent yet attached to anything, thats all worked out by the SessionContext extension, and optionally the get_session() method on MapperExtension. this allows you to pull up a session from a class' mapper which is based on *some* context, of which you can define to be whatever you want. that whole thing is described at http:// www.sqlalchemy.org/docs/plugins.myt#plugins_sessioncontext . typically the context is that Sessions are keyed to the identifiers of threads, since the Session is generally not threadsafe. On Jul 13, 2006, at 2:52 PM, Randall Smith wrote: > I see. Would it be bad design to give an SA class instance a session > attribute or something similar? Not having it limits some work on > that > object to the current scope. Consider this: > > import util > from sqla_classes import TestClass > > session = create_session(...) > obj = session.query(TestClass).select()[0] > util.doStuff(obj) > > The doStuff method of util does not have access to session unless > passed > explicitly. It would be convenient if obj knew what session it was a > part of. Maybe that would introduce some problems. I don't know. > Unless it has been detached, it should be in a session. > > I frequently find myself wanting to get the session or engine from > an SA > class instance because it's inconvenient or difficult to get the > session > or engine otherwise and I don't want to make my code dependent on how > the connection is implemented. For example, this > > class_mapper(someclass).mapped_table.metadata.engine > > will only succeed if I connected metadata to the engine. I may decide > part way through a project to connect via create_session > (bind_to=engine) > and my code would break. > > Randall > > > Michael Bayer wrote: >> if you dont have a session to work with then youd just use >> connections off the engine being used. >> >> if you have your engines bound to tables and you want to get at that >> via the mapped class, first off id say why not just have the engine >> by itself somewhere? but if you really need to, it looks like >> >> class_mapper(someclass).mapped_table.metadata.engine >> >> for some examples about how to mix connections/sessions/transactions, >> see >> >> http://www.sqlalchemy.org/docs/unitofwork.myt#unitofwork_transaction >> http://www.sqlalchemy.org/docs/ >> unitofwork.myt#unitofwork_transaction_sql >> http://www.sqlalchemy.org/docs/ >> unitofwork.myt#unitofwork_transaction_using >> > > > > ---------------------------------------------------------------------- > --- > Using Tomcat but need to do more? Need to support web services, > security? > Get stuff done quickly with pre-integrated technology to make your > job easier > Download IBM WebSphere Application Server v.1.0.1 based on Apache > Geronimo > http://sel.as-us.falkag.net/sel? > cmd=lnk&kid=120709&bid=263057&dat=121642 > _______________________________________________ > Sqlalchemy-users mailing list > Sqlalchemy-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/sqlalchemy-users ------------------------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 _______________________________________________ Sqlalchemy-users mailing list Sqlalchemy-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/sqlalchemy-users
