Haven't tested it, but the "pre_add" and "pre_remove" actions in the m2m_changed signal should be triggered before the change, and they include a pk_set arg with the id's of the related M2M model being added / removed.
You could also link to the post_save and post_remove which contain the same flag, but that depends on what are you trying to accomplish. On Sun, Mar 8, 2015 at 8:15 PM, Fabien Schwob <xphut...@gmail.com> wrote: > With the m2m changed signal I can only have the state of the object after > it has been saved. Not the difference between before and after the change. > On sam. 7 mars 2015 at 16:53 Vijay Khemlani <vkhem...@gmail.com> wrote: > >> You might find the m2m_changed signal useful >> >> https://docs.djangoproject.com/en/1.7/ref/signals/#m2m-changed >> On Sat, Mar 7, 2015 at 7:57 AM, Fabien Schwob <xphut...@gmail.com> wrote: >> >>> Hello, >>> >>> I would like to detect changes in a ManyToMany field, to update data >>> in the linked Model. I've two objects : >>> >>> class Category(models.Model): >>> .... some fields ... >>> >>> >>> class Post(models.Model): >>> .... some fields ... >>> categories = models.ManyToManyField(Category) >>> >>> And I would like to detect (in the admin and when accessing the object >>> in python) when categories are added or removed to a Post. To update >>> some fields in the Category model. But I've tried with : >>> >>> * django.db.models.signals.m2m_changed, but it doesn't appear to be >>> trigged in the admin >>> * by overriding Post.save(), but I get the same information before >>> and after the save() (I think it's because m2m are handled after >>> save() has finished) : >>> >>> def save(self, *args, **kwargs): >>> print Post.objects.get(pk=self.id).categories.all() >>> super(Post, self).save(*args, **kwargs) >>> print Post.objects.get(pk=self.id).categories.all() >>> >>> Any solutions to handle this case ? With a custom signal, or anything >>> else ? >>> >>> Thanks >>> -- >>> Fabien Schwob >>> >> -- >>> >> You received this message because you are subscribed to the Google Groups >>> "Django users" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to django-users+unsubscr...@googlegroups.com. >>> To post to this group, send email to django-users@googlegroups.com. >>> Visit this group at http://groups.google.com/group/django-users. >>> To view this discussion on the web visit >>> https://groups.google.com/d/msgid/django-users/CAL%3DxoZRnd7812MykJSsh3Avhh%2BiFk9J3g9nkhv61UA%3D4a9j8Ow%40mail.gmail.com >>> <https://groups.google.com/d/msgid/django-users/CAL%3DxoZRnd7812MykJSsh3Avhh%2BiFk9J3g9nkhv61UA%3D4a9j8Ow%40mail.gmail.com?utm_medium=email&utm_source=footer> >>> . >>> For more options, visit https://groups.google.com/d/optout. >>> >> -- >> You received this message because you are subscribed to the Google Groups >> "Django users" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to django-users+unsubscr...@googlegroups.com. >> To post to this group, send email to django-users@googlegroups.com. >> Visit this group at http://groups.google.com/group/django-users. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/django-users/CALn3ei0-ZNc2je48jNdt_E78jK%2BO-HCO8zpKyb3%2BtCMx0Ee9Xw%40mail.gmail.com >> <https://groups.google.com/d/msgid/django-users/CALn3ei0-ZNc2je48jNdt_E78jK%2BO-HCO8zpKyb3%2BtCMx0Ee9Xw%40mail.gmail.com?utm_medium=email&utm_source=footer> >> . >> For more options, visit https://groups.google.com/d/optout. >> > -- > You received this message because you are subscribed to the Google Groups > "Django users" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to django-users+unsubscr...@googlegroups.com. > To post to this group, send email to django-users@googlegroups.com. > Visit this group at http://groups.google.com/group/django-users. > To view this discussion on the web visit > https://groups.google.com/d/msgid/django-users/CAL%3DxoZQbykrPHhdeo8vVr2rD0R4owVhP%2Bd7OZ9fCux4qqStVNg%40mail.gmail.com > <https://groups.google.com/d/msgid/django-users/CAL%3DxoZQbykrPHhdeo8vVr2rD0R4owVhP%2Bd7OZ9fCux4qqStVNg%40mail.gmail.com?utm_medium=email&utm_source=footer> > . > > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "Django users" group. To unsubscribe from this group and stop receiving emails from it, send an email to django-users+unsubscr...@googlegroups.com. To post to this group, send email to django-users@googlegroups.com. Visit this group at http://groups.google.com/group/django-users. To view this discussion on the web visit https://groups.google.com/d/msgid/django-users/CALn3ei0DMpjtp0qdf1nFh%3Dht8j2DY7urrEx6fHytMLxshAwihA%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
