Re: for loop + transaction.on_commit + celery = Unexpected Behaviour

This is an older topic, but for everyone who found this discusion and had the same issue: The problem is most likely using "lambda" inside a for-loop. If you switch out "lambda" for "functools.partial" it should work as expected.

Jani Tiainen schrieb am Donnerstag, 27. April 2017 um 08:27:11 UTC+2:

Hi,

I think your problem is to use POST['_models_changed']. Django uses specialized version of dictionary there which return _last_ value from list. You need to use special "get_list()" method to get whole list of objects.

Your code should start working if you do data['_models_changed'].get_list()  in a for-loop.

Also, why you modify request.POST instead of adding class attribute?

On 24.04.2017 14:37, Emilio Jimenez Canalejo wrote:

Hi, I've been looking for some time around the internet a problem I have, maybe I'm just dull from all the searching and the answer is pretty obvious, but I can't find it.

For example, I have code like this:

@app.task
def foo(idx):
    print("This is iteration {}".format(idx))

def save_model(self, request, obj, form, change):
    data = request.POST
    result = super(Model, self).save_model(request, obj, form, change)

    for pk in data['_models_changed']:
        transaction.on_commit(lambda: foo(pk))

To my astonishment, I thought I would get:

"This is iteration 1"
"This is iteration 2"
"This is iteration 3"
"This is iteration 4"

But I got:

"This is iteration 4"

"This is iteration 4"

"This is iteration 4"

"This is iteration 4"

I'm using python 2.7, Django 1.10.5 and Celery 4.0.2.

'models_changed' is a field in the post added by a custom clean method.

Anyone knows a way to do this?

Thanks for all!

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