On Sep 12, 2010, at 11:02 PM, alex bodnaru wrote: > thanks a lot michael. > indeed it works, but it seems counter-intuitive a little since passive_* > should > in my opinion be on the side of the on * cascade it describes. > anyway, it's great, and hope to make it work with elixir too.
If you said session.delete(my_other_object), no action is needed if it references some particular my_object. It is only if you session.delete(my_object) that SQLAlchemy needs to do something - and for that, it must load those objects which reference my_object. It does this simply by using the one-to-many collection on my_object which states how to load my_other_objects with an association. So the one-to-many collection is what's needed here - if you only specified the other direction, SQLAlchemy would need to derive the forwards collection from it and apply it to the o2m parent class internally. Right now the internals are simple such that loading is only possible in the direction in which the relationship() was configured. It is certainly possible to alter relationship() to be able to load collections or associations in both directions so that a many-to-one relationship could transparently load from the other direction, though internally this would require doing pretty much what "backref" does explicitly - placing some linkage to the relationship on the target class of the many-to-one which could react to deletions of that target class. So the current implementation is much simpler than that, so the "passive_updates" flag goes onto the side of the relationship that ultimately needs it, so that SQLAlchemy doesn't need to "generate" the backref which is easy enough for the user to specify, and in very rare conditions may even be configured differently than the reverse direction. The original design of "cascade" is taken from Hibernate, probably the most widely used object relational tool in history. They too tend to define ORM-level information about the "foreign key", including the CASCADE attributes on the primary key side: http://docs.jboss.org/hibernate/stable/core/reference/en/html/mapping.html#mapping-declaration-key http://docs.jboss.org/hibernate/stable/core/reference/en/html/collections.html#collections-mapping > > -- > You received this message because you are subscribed to the Google Groups > "sqlalchemy" group. > To post to this group, send email to sqlalch...@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. > -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to sqlalch...@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.
