On Thu, Feb 11, 2016 at 6:59 PM, dieter <die...@handshake.de> wrote: > In my context (web applications), I strongly discourage this use - at least > when "conn" does not handle subtransactions properly. > > In a web application, the main transaction should in general be controlled > at the request level: a request should either succeed as a whole or have no > side effects whatsoever. This prohibits local (somewhere > deep in a component) transaction control.
Hmm. I'm not 100% convinced that web apps should behave that way; but part of the simplicity comes from requiring that database-dependent code should not call other database-dependent code, as that would create a nested transaction. (That said, though, it's entirely possible that psycopg2 could handle a nested "with conn" as "SAVEPOINT" and either "RELEASE SAVEPOINT" or "ROLLBACK TO SAVEPOINT". But I wouldn't recommend depending on that without confirming it in the docs.) Bear in mind, the rule I gave was a broad and general rule for students to follow, not a hard-and-fast rule for all databasing. It's designed such that the student can learn the exceptions later on, but meanwhile, his code will be correct (if occasionally a little warped to avoid nesting transactions). ChrisA -- https://mail.python.org/mailman/listinfo/python-list
