On Mar 8, 2012, at 4:23 PM, ypg wrote: > I am running SQLAlchemy under a multithreaded python server (paster), > as part of a web application which is written using the Python Pyramid > framework. When I modify an existing database entry through SQL > alchemy, subsequent page refreshes seem to randomly pick between the > original instance of the object, and the modified copy. > > For example: if I have user object where user.username is "jdoe", and > I change the username to "rickymartin", and then keep refreshing the > page, I will randomly see the "jdoe" and "rickymartin", as the > username. If I then change the username again to "shakira", and > continue to refresh the page, I will randomly see "shakira" or > "rickymartin". If I check the database independently, or if I restart > the web server, I will only ever see updated version of the username. >
SQLAlchemy maintains the value of columns within attributes loaded in a single Session. It's not a strict form of caching, in that it isn't caching the results of queries, but for the span of an object in the identity map within a particular transaction it will hold onto loaded attribute values. The refresh issue sounds like you have Sessions hanging open with uncommitted and/or stale data in them, and depending on which thread you get, you see either older or newer data. Make sure you commit all pending data at the end of a request and then make sure you close out the session at the end of each request. Start each new request with brand new Session. Some overview of this at http://docs.sqlalchemy.org/en/latest/orm/session.html#lifespan-of-a-contextual-session > I am using a single scoped_session instance to create the sessions, > which is global to all the threads running in the web application. I > can solve this issue by creating a new session every time a request > comes in, but that would make the code a bit sloppy and I'm trying to > avoid doing that. Well that's the cause here, and interesting you consider allocating new resources at the start of a request and cleaning them up at the end "sloppy". I'd view this as exactly the opposite, leaving remnants of a previous request hanging around would be the definition of sloppiness IMHO. Pyramid supports clean patterns for establishing Session lifespan with the zope.transaction extension - you should check their docs and their mailing list for guidelines on its usage. -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to sqlalchemy@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.
