Ah yes, that should have been Foo(), not Foo. I think I have it under control for now. I'll try using the debug info if I run into any more problems.
Thanks. Cameron Jackson Engineering Intern Air Operations Thales Australia Thales Australia Centre, WTC Northbank Wharf, Concourse Level, Siddeley Street, Melbourne, VIC 3005, Australia Tel: +61 3 8630 4591 cameron.jack...@thalesgroup.com.au<mailto:cameron.jack...@thalesgroup.com.au> | www.thalesgroup.com.au<http://www.thalesgroup.com.au> From: sqlalchemy@googlegroups.com [mailto:sqlalchemy@googlegroups.com] On Behalf Of Michael Bayer Sent: Tuesday, 20 December 2011 2:07 AM To: sqlalchemy@googlegroups.com Subject: Re: [sqlalchemy] Multiple sessions and data conflicts. On Dec 19, 2011, at 1:04 AM, Jackson, Cameron wrote: OK, I think I understand. Just to make sure, how about this example: from SomeModule import Session, Foo session1 = Session() session2 = Session() data1 = session1.query(Foo).all() data2 = session2.query(Foo).all() data1[0].bar = 'Baz' data1.append(Foo) session1.add(data1[-1]) session1.commit() session2.rollback() data2 = session2.query(Foo).all() After all of that, data2[0].bar should equal 'Baz', and data2[-1] should be the new Foo that we created and added to data[1], correct? In other words, the contents of data1 and data2 should be identical, right? well you wouldn't be appending the "Foo" class so I assume there's some paraphrasing going on, but the general idea that s1 is committed, then s2 rolled back, s2 would emit SQL for everything yes. "identical" as I said would go as far as ORM-mapped attributes. Using echo='debug' with your engine is the best way to sanity check this stuff. Cheers, Cameron Jackson Engineering Intern Air Operations Thales Australia Thales Australia Centre, WTC Northbank Wharf, Concourse Level, Siddeley Street, Melbourne, VIC 3005, Australia Tel: +61 3 8630 4591 cameron.jack...@thalesgroup.com.au<mailto:cameron.jack...@thalesgroup.com.au> | www.thalesgroup.com.au<http://www.thalesgroup.com.au/> From: sqlalchemy@googlegroups.com<mailto:sqlalchemy@googlegroups.com> [mailto:sqlalchemy@googlegroups.com] On Behalf Of Michael Bayer Sent: Monday, 19 December 2011 12:51 PM To: sqlalchemy@googlegroups.com<mailto:sqlalchemy@googlegroups.com> Subject: Re: [sqlalchemy] Multiple sessions and data conflicts. On Dec 18, 2011, at 8:25 PM, Jackson, Cameron wrote: Here is a simplified version of my scenario: My application has two session objects. One is being used for editing certain data, and the other is reading this data, doing some calculations, and displaying the results. I've set up a callback kind of system so that whenever the first session does a commit, a method is called that does a rollback on the second session, and redoes the calculations and display. I've had bugs crop up where the data I get from querying the second session object doesn't match what I know is in the database, but I haven't been able to reproduce them consistently yet. So my questions are: 1. After a session.rollback(), should the data obtained from that session's queries match what's in the DB now? Or what was in the DB when the session was created? The docs<http://www.sqlalchemy.org/docs/orm/session.html#sqlalchemy.orm.session.Session.rollback> are not clear on this. 2. If a rollback is not enough to guarantee that the data from querying a session is up to date, then what is? Should I just create a new session entirely? These are the comprehensive docs on rollback: http://www.sqlalchemy.org/docs/orm/session.html#rolling-back A rollback expires all attributes that are database mapped, on objects that are persistent within the session. Touching any of these attributes subsequent to the expire will cause them to emit SQL to get the new value back. You might not see what you expect if A. you're accessing an object that isn't persistent within that session, such as one that was "new" before the rollback, as these get evicted after rollback, or B. you're looking at your own attributes which aren't directly database mapped. As far as "what's in the DB", a new transaction starts after rollback, and that's against whatever has been committed to that DB. If your other transaction hasn't committed then you wouldn't see its data. cheers, Cam Cameron Jackson Engineering Intern Air Operations Thales Australia Thales Australia Centre, WTC Northbank Wharf, Concourse Level, Siddeley Street, Melbourne, VIC 3005, Australia Tel: +61 3 8630 4591 cameron.jack...@thalesgroup.com.au<mailto:cameron.jack...@thalesgroup.com.au> | www.thalesgroup.com.au<http://www.thalesgroup.com.au/> ------------------------------------------------------------------------- DISCLAIMER: This e-mail transmission and any documents, files and previous e-mail messages attached to it are private and confidential. They may contain proprietary or copyright material or information that is subject to legal professional privilege. They are for the use of the intended recipient only. Any unauthorised viewing, use, disclosure, copying, alteration, storage or distribution of, or reliance on, this message is strictly prohibited. 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