On Apr 11, 2012, at 12:22 PM, Franck wrote:
> Hi Mike,
>
> Thanks for your prompt answer !
>
> Thanks for fixing my "default" field - makes complete sense.
> Besides I added the "vote_dt" assignment in the PollVote constructor but it
> seems that this constructor is called only once, i.e. after the first
> "result_values_by_user" assignment : poll.result_values_by_user[joe] =
> set(["A", "B", "C"])
>
> It seems that the 2 further "result_values_by_user" assignments don't trigger
> the constructor - please see the SQL trace below. What I'm trying to achieve
> is to automatically update this date not only at row creation time, but also
> when the underlying collection is modified.
>
> Am I missing something here ?
OK so look at the terminiology - "update this date" - you're looking for an
UPDATE to the row, so an __init__ does not correspond to that. Sometimes we
do on-updates at the SQL level using "onupdate", but that's to respond to
something else being updated. In this case, you want the date on POLL_VOTES
updated whenever its related POLL_RESULTS entries change as well (right ?) -
so to get every kind of change on an attribute we can use attribute events:
from sqlalchemy import event
@event.listens_for(PollVote.results, "append")
@event.listens_for(PollVote.results, "remove")
@event.listens_for(PollVote.results, "set")
def _on_vote(target, value, initiator):
target.vote_dt = datetime.datetime.now()
I think I'm going to beef up the @validates decorator, which is a convenience
decorator for the above, to include the ability to intercept deletes.
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