Cant get post_save to work in Django

Question

I read the django docs about signals and wrote this piece of code for my model Car :

@receiver(request_finished)
def signal_callback(sender, **kwargs):
    print 'Save Signal received'


@receiver(post_save, sender=Car)
def signal_handler(sender, **kwargs):
    pass


request_finished(signal_callback, sender=car, dispatch_url="Unique save id")

But the problem is, that when I fire up my server, and just open up the admin, I get a lot of 'Save Signal received' in my terminal. What I am wondering about is I have restricted the signal_handler to post_save only. But still, without even saving anything, the message shows up a lot of times. I dont understand this.

Note : I will be honest. I understood parts of it, not everything from the documentation.

score 5 · Accepted Answer · edited Jan 26 '17 at 23:16

There is a simpler way to bind post_save signals

from django.db.models.signals import post_save
from myapp.models import Car

def do_something(sender, **kwargs):
    print 'the object is now saved.'
    car = kwargs['instance'] #now i have access to the object

post_save.connect(do_something, sender=Car)

The signal request finished gets called every time a HTTP request is made, which is a hog.

score 2 · Answer 2 · answered Jun 23 '13 at 05:31

2

You binded request_finished signal to signal_callback. Remove(or comment out) signal_callback, and change signal_handler as follow.

@receiver(post_save, sender=Car)
def signal_handler(sender, **kwargs):
    print 'Save signal received'

answered Jun 23 '13 at 05:31

falsetru

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and then I should bind `request_finished` with `signal_handler` ? – Indradhanush Gupta Jun 23 '13 at 05:33
then what about the method thats supposed to send the signal? – Indradhanush Gupta Jun 23 '13 at 05:37
`signal_handler` is called when `Car.objects.create(...)` or `Car(...).save()` is called. – falsetru Jun 23 '13 at 05:39
yeah that works. but I don't grasp it very well. Is it like `request_finished` sending the signal when its saved and `signal_handler` catching it? – Indradhanush Gupta Jun 23 '13 at 06:09
`request_finished` is not relevant to save. request_finished signal is fired when http request is handled. – falsetru Jun 23 '13 at 06:19
no, the `request_finished` signal is fired when the model is done saving itself not when the http request is handled. – Henrik Andersson Jun 23 '13 at 06:59
@limelights, https://docs.djangoproject.com/en/dev/ref/signals/#django.core.signals.request_finished – falsetru Jun 23 '13 at 07:03
@falsetru My fault, I read the question too fast. You are 100% correct! – Henrik Andersson Jun 23 '13 at 07:05
@falsetru so when the http request is complete, it checks whether its a `save` or not, and then calls the `signal_handler`. Is this the process? – Indradhanush Gupta Jun 23 '13 at 07:13
@falsetru hey I've done what you have said. So when `signal_handler` is called, the object is supposed to be `saved` right. I am running the code in `pdb` and upon inspecting, I see that the `many-to-many` element isnt getting saved. In the `next save` operation of the "same object", the previous data appears and the new data that has been added, doesnt. Any specific reason you think? – Indradhanush Gupta Jun 23 '13 at 07:20
@IndradhanushGupta, Please post another question with **code**. – falsetru Jun 23 '13 at 07:46
@falsetru The new question : http://stackoverflow.com/questions/17263780/many-to-many-field-not-shown-in-object-while-using-signals-to-detect-save-operat – Indradhanush Gupta Jun 23 '13 at 18:21

Cant get post_save to work in Django

2 Answers2

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