using relationship() with collection_class=set, assuming User, User.preferences
-> Pref, just assigning to the collection will replace the previous contents
with the new one:
myuser.preferences = set([Pref("A"), Pref("C")])
B and D go into the "removed" list, A and C are "pending", on flush you'll see
the rows managed. If User->Pref is one-to-many, that is Pref is "owned" by
just one user, use cascade="all, delete-orphan" - Pref B and D will be deleted
on flush.
On Apr 2, 2012, at 7:32 AM, Franck wrote:
> Hi,
>
> To store the preferences of my users I'm storing one row per user &
> per preference : if the possible choices are A,B,C,D I'm storing B,C,D
> for instance at the user level in the database.
> Suppose the user changes its preferences and picks A,C for instance.
>
>> I'm going to need to delete B & D
>> I'm going to need to persist A
>
> I was thinking to do this manually with the builtin set operations
> (http://docs.python.org/library/stdtypes.html#set), typically
> "difference", to manually add/remove these in the session but is there
> a way SQLAlchemy can do the work for me automatically ?
>
> Thanks !
> Franck
>
>
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