In the MySQL system I'm redoing with SQLAlchemy, there is effectively a "master' schema that exists once top-level stuff (including a table describing projects) , and "project" schemas (one identical set of tables per project), which have project-level stuff. When an object is retrieved from a project, there is nothing in the data itself which indicates which project it was loaded from, but this may in certain cases be needed. I have a nice collection of Project objects loaded from the master schema lying around, and I pass my own subclass of SQLA's Session to sessionmaker() so I can store a reference to the appropriate Project with a session. But since Detached and Transient instances don't have an associated session, I can't just use object_session() to access the Project via the instance's session. So I thought I'd stamp a reference to the appropriate Project onto instances.
SQLA's event system has the "after_attach" session event. Hooking into this works for new instances I attach to a session with add(), but does't fire when items are loaded from a query - presumably "attached" means direct userland attachment only, not instances being associated with a session via a query. So it's only half the solution - there doesn't seem to be a session-level event that fires in the latter case? There is a "load" instance-level event, which seems to solve the other half of this. The QueryContext passed to the handler contains the session, and I can stamp the instance with the Project reference I've stored in the session. The only drawback is that I apparently need to separately attach the event listener to each project instance class? Presumably I could somehow retrieve a list of classes from the declarative_base (_decl_class_registry_ ?) and walk through that adding the listeners. Is this a reasonable approach, and between the two events I'll be seeing all the objects that enter the session either from database retrieval or my code? -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To view this discussion on the web visit https://groups.google.com/d/msg/sqlalchemy/-/_F71NtWi9MsJ. 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.
