On Sep 24, 2012, at 1:48 PM, Mahmoud Abdelkader wrote: > I wanted to know some views about the soft-delete (anti?) pattern and whether > or not I'm going about it the right way in my code base. > > We have a piece of code: > > class NoDeletedQuery(Query): > def __new__(cls, *args, **kwargs): > if args and hasattr(args[0][0], "deleted_at"): > return Query(*args, **kwargs).filter_by(deleted_at=None) > else: > return object.__new__(cls) > > > Session = scoped_session(sessionmaker(query_cls=NoDeletedQuery)) > > This is pretty obvious, just auto adds a filter that ignores the deleted at, > but, I think this is a very hard thing to get right, especially with joins > and whatnot. This works, but I would like to know what's the recommended > idiom? I looked at this stack overflow question: > > http://stackoverflow.com/questions/920724/the-right-way-to-auto-filter-sqlalchemy-queries
the recipe we have in this regard is similar and is here: http://www.sqlalchemy.org/trac/wiki/UsageRecipes/PreFilteredQuery however, it is still pretty simplistic and doesn't produce the sub-selectable you prefer here. A hybrid of both approaches can be achieved with select_from(): class SomeQuery(Query): def __new__(cls, *arg, **kw): if (<we should use deleted_at>): return Query(*arg, **kw).select_from(select([table]).where(table.c.deleted_at==None).alias()) else: return object.__new__(cls) that is, query(cls).select_from(selectable) is roughly equivalent to having a mapper() against "cls" that's mapped to "selectable". Though the ORM still uses query() internally and I'm not sure that will get around the object deleted exception you're getting. It's also not clear why you'd be getting that exception anyway, unless you are trying to access an object which corresponds to a row that's marked "deleted". Only a full stack trace and preferably a simple reproducing case would show exactly why it's getting there. -- 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.
