On Jan 26, 2012, at 11:28 AM, Kent Bower wrote: > I think I understand why, during a flush(), if I use session.query().get() > for an item that was just added during this flush, I don't get the persistent > object I might expect because the session still has it as pending even > though, logically, it is already persistent. > > I don't suppose you have any desire to support that, huh? The use case would > be related to the future ticket http://www.sqlalchemy.org/trac/ticket/1939 > (and http://www.sqlalchemy.org/trac/ticket/2350). > > Attached is a script demonstrating the issue I've hit. I can work around it > with some difficulty, but I wanted your input and thoughts.
No, there's no plans to support this case at all; you're using the Session inside of a mapper event, which is just not supported, and can never be due to the nature of the unit of work. The most recent docstrings try to be very explicit about this: http://docs.sqlalchemy.org/en/latest/orm/events.html#sqlalchemy.orm.events.MapperEvents.before_update I guess I have to add session.query() and get() in there as well. The way the flush works is not as straightforward as "persist object A; persist object B; persist object C" - that is, these are not atomic operations inside the flush. It's more like, "Perform step X for objects A, B, and C; perform step Y for objects A, B and C". This is basically batching, and is necessary since it is vastly more efficient than atomically completing each object one at a time. Also, some decisions are needed by Y which can't always be made until X has completed for objects involved in dependencies. A side effect of batching is that if we provide a hook that emits after X and before Y, you're being exposed to the objects in an unusual state. Hence, the hooks that are in the middle like that are only intended to emit SQL on the given Connection; not to do anything ORM level beyond assigning column-based values on the immediate object. As always, before_flush() is where ORM-level manipulations are intended to be placed. -- 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.
