Why does Django post_save signal give me pre_save data?

Question

Im trying to connect a "Information" object to many "Customers" (see code below)

When one Information object is updated, I want to send email to each Customer that is connected to the Information.

However, when I log the sold_to field that the signal recieves I always get what the data is like BEFORE the save.

I'm guessing this is because its ManyToManyField and the data is stored in a separate table, but shouldn't the post_save signal be called after all relations have been updated?

Anyone got a suggestion for a solution?

class Customer
    name = models.CharField(max_length=200)
    category = models.ManyToManyField('Category',symmetrical=False)
    contact = models.EmailField()

class Information
    name = models.CharField(max_length=200)
    email = models.EmailField(max_length=200)
    mod_date = models.DateTimeField(auto_now=True)
    sold_to = models.ManyToManyField(Customer, null=True, blank=True)


def send_admin_email(sender, instance, signal, *args, **kwargs):
    from myapp import settings
    for cust in instance.sold_to.all():
        settings.debug(cust.name)

post_save.connect(send_admin_email, sender=Information)

Edit: apollo13 in #django alerted me to this: "Related items (the things being saved into the many-to-many relation) are not saved as part of a model's save method, as you have discovered." - http://groups.google.com/group/django-users/msg/2b734c153537f970

But since its from Jul 9 2006 I really really hope there is a solution for this.

Answer 1

There's an open ticket for the issue you are facing here. You could either keep an eye on that for when it makes it into a release, or you could try applying the patch that it provides and see if that helps.

Answer 2

This is my solution, after applying the patch from code.djangoproject.com mentioned above.

Added this in models.py:

from django.db.models.signals import m2m_changed
m2m_changed.connect(send_admin_email, sender=Information)

And the send_admin_email function:

def send_customer_email(sender, instance, action, model, field_name, reverse, objects, **kwargs):
    if ("add" == action):
        # do stuff