On Nov 25, 2013, at 9:00 AM, George Sakkis <george.sak...@gmail.com> wrote:
> Hi all,
>
> is there a feature or pattern for adding a listener that is to be executed
> (at most) once? For example, say you want to send an email when user is
> created and the session is committed. If event.listen() supported a "once"
> boolean parameter, this could be expressed as:
>
> def email_user(email_address, message):
> ...
> ...
> if valid_data:
> new_user = User(**valid_data)
> db.session.add(new_user)
> # send an email to new_user after committing
> event.listen(db.session, "after_commit",
> once=True, # hypothetical parameter
> lambda session: email_user(new_user.email, "welcome
> {}!".format(new_user.name))
there are certain events such as pool.first_connect that use a “once” type of
system, but that is linked to the type of event.
I haven’t tried this but you should be able to call event.remove() (sqlalchemy
0.9) within the handler:
def go(session):
email_user(…)
event.remove(session, “after_commit”, go)
event.listen(session, “after_commit”, go)
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