Cannot insert entries when using an eager Join multiple times to one table

(original reporter: rtl) When using an eager join multiple times to one table as shown in the documentation and attempting to add a new address to the boston (or new york) addresses, i.e. u.boston_addresses.append(Address(..from Boston)), when commit() is run it is failing because the foreign key of the new address (i.e. user_id) has not been set.