On Oct 6, 2010, at 6:46 AM, Warwick Prince wrote: > > I can't quite get my head around the "scope" of sessionmaker() yet.. I've > tried putting Session = sessionmaker() as a global to the entire codebase > (works but has same problem)
do you mean scoped_session here ? sessionmaker is just a constructor for a new Session. It doesn't hold onto anything. scoped_session OTOH is nothing more than a thread local variable. Background on this concept is available here: http://docs.python.org/library/threading.html#threading.local . The remove() call removes the current thread local's context. If your app were single threaded, you could replace it with a single Session object, where you just call close() instead of remove() - it wouldn't be very different. Within the context of a multiprocess, single-threaded application, threading.local doesn't have any effect - there's just one thread. > Importantly.. I can completely close all my processes and cold start my code > - and this error continues until I restart mySQL ! i.e. NO session will work > again, but I can do basic queries. What the?! I've seen this happen with PG when we are testing out two-phase transactions. You might want to ask on some MySQL forums what queries you might do to look at current lock/transaction state. > > BTW: It someone says "You should be using scoped_session.." Please explain > how to have either more than one session in the same context (I use three for > a possible three different binds) yeah I actually have an app with a couple of scoped sessions, since there are two different databases and operations generally proceed with one or the other. > or how to create one session that I can bind to more than one engine, and not > have to know in advance all possible tables I might want to use on each > engine.. If the table metadata is bound to an engine, then the session doesn't need to be bound. I.e. if tables A, B, C on metadata X are bound to engine P, tables D, E, F on metadata Y are bound to engine Q, you just use the Session, and it will handle the two engines as needed. If you really want total control, using some ruleset that's not quite as simple as table->metadata->engine, you can subclass Session and override get_bind(). I've never recommended that to anyone, but I put it out there just to help de-mystify the situation. Its just one call that takes in a mapper, returns an engine. -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to sqlalch...@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
