On Fri, Mar 3, 2017 at 8:34 AM, Michael Merickel <mmeri...@gmail.com> wrote: > On Fri, Mar 3, 2017 at 10:10 AM, Mike Orr <sluggos...@gmail.com> wrote: >> >> The biggest problem with pyramid_tm I've run into is wanting to >> rollback or commit the accumulated changes within the view without >> messing up the global transaction outside the view. Normally when you >> commit SQLAlchemy starts a new transaction afterward, but with >> pyramid_tm you have to use 'transaction.commit' and that messes up its >> transaction for the rest of request processing. > > > Isn't this what savepoints are for? > > def view(request): > sp = request.tm.savepoint() > try: > # view things ... > > # finally flush to push changes to the db without committing... this > will > # raise any IntegrityError, etc > request.dbsession.flush() > except Exception: > # go back to where we were before the view executed > sp.rollback()
Ah, I didn't realize you could do that. > Obviously a lot of people are confused on this point, and that's an issue. > The most common cases are usually solved by some combination of savepoints > and flushing the underlying database session to catch errors earlier. For > example, SQLAlchemy buffers all of your edits until a flush, and if you > don't do it manually then it waits until commit. You could catch them > earlier if you did a request.dbsession.flush() in a try/except (probably > around a savepoint). The issue is that you may set up 'pyramid_tm' because the normal case applies 99% of the time and seemingly always, and then you already have an application built and discover that one view needs something more complex. I'll try savepoints and see if that solves it. As for flush, there's a problem in the opposite direction. If you don't flush then you can expunge pending adds/deletes from the session and it's like they never were there. But if you do flush (e.g., to get an autoincrement ID or fill in server-side defaults), then you can't simply expunge them, you have to roll back. And if you've written a library function that flushes, you can't get around the flush without bypassing or rewriting the function. -- You received this message because you are subscribed to the Google Groups "pylons-discuss" group. To unsubscribe from this group and stop receiving emails from it, send an email to pylons-discuss+unsubscr...@googlegroups.com. To post to this group, send email to pylons-discuss@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/pylons-discuss/CAH9f%3DurQY%2BS2Pmccq2uQzT5gED%3D0NARLoQxmTYMpNKVSY5umSA%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
