Re: Signal handling when deleting lots of objects?

> Den 1. sep. 2016 kl. 20.14 skrev Stodge <stodge@gmail.com>:
>
> I have two models, Volume and Group. The Volume model has a foreign key to Group.
>
> When a user deletes a Volume the post_delete signal handler sends an HTTP DELETE request (/volume) to another server process. This works great. However, when the user deletes a Group, the cascading delete also deletes all volumes in that group. That means I get lots (I'm talking <100) of post_delete signals for the Volume model and therefore lots of HTTP requests.
>
> Is there anyway to avoid this? Ideally, I'd like to send the HTTP DELETE request (/volume) when a volume is deleted, but send a different HTTP DELETE request (/group) when the group is deleted and avoid sending any volume HTTP DELETE requests.

You could disconnect the post_delete signal for Volume temporarily, but that's a hack.

You probably have to abandon signals on the Volume model. I would attach the post_delete signals logic directly to the Volume.delete() method and add an option to disable signaling:

class Volume(models.Model):
[....]
def my_signal_logic(self):
do_whatever()

def delete(self, *args, **kwargs):
with_signal = kwargs.pop('signal', True)
if with_signal:
self.my_signal_logic()
super().delete(*args, **kwargs)


Then in the post_delete signal for Group, you delete the Volumes explicitly, telling delete() not to signal:

for v in instance.volumes.all():
v.delete(signal=False)

requests.delete('/group/%s' % instance.pk)


Erik

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