django model override save m2m field - django

Question

I want to update m2m field on save() method
I have the following model:
class Tag(models.Model):
label = models.CharField(max_length=50)
parents_direct = models.ManyToManyField("Tag", related_name="children", blank=True)
created = models.DateTimeField(auto_now_add=True)
description = models.TextField(null=True, blank=True)
administrators = models.ManyToManyField(
to=KittyUser, related_name="administrated_tags", blank=True)
moderators = models.ManyToManyField(
to=KittyUser, related_name="moderated_tags", blank=True)
allowed_users = models.ManyToManyField(
to=KittyUser, related_name="allowed_tags", blank=True)
visible = models.BooleanField(default=True, verbose_name="visible to anyone")
POSTABILITY_CHOICES = (
('0', 'any allowed user can post'),
('1', 'only moderators\\admins can post')
)
postability_type = models.CharField(default='0',
max_length=1,
choices=POSTABILITY_CHOICES)
parents_tree = models.ManyToManyField("Tag", related_name="parents_tree_in_for", blank=True)
related_tags = models.ManyToManyField("Tag", related_name="related_tags_in_for", blank=True)
def save(self, *args, **kwargs):
self.label="overriden label"
super(Tag, self).save(*args, **kwargs)
self.parents_tree.add(*self.parents_direct.all())
breakpoint()
super(Tag, self).save(*args, **kwargs)
Through django-admin the tags get created, the label substitution works, though parents_tree don't get updated.
If I create it from the shell, it is swearing at the second super().save:
django.db.utils.IntegrityError: duplicate key value violates unique constraint "posts_tag_pkey"
If you take away the first super.save(), you get the following:
"<Tag: overriden label>" needs to have a value for field "id" before this many-to-many relationship can be used.
in both shell and admin.
The question is, how to update my m2m field on save?
Another question is why does it work differently in admin panel and shell?
As a temporary solution I managed to listen to the signal of updating parents_direct field, but what if I wanted to depend on non-m2m fields?
from django.db.models.signals import m2m_changed
def tag_set_parents_tree(sender, **kwargs):
if kwargs['action'] == 'post_add' or 'post_remove':
parents_direct = kwargs['instance'].parents_direct.all()
if parents_direct:
kwargs['instance'].parents_tree.set(parents_direct)
for tag in parents_direct:
kwargs['instance'].parents_tree.add(*tag.parents_tree.all())
else:
kwargs['instance'].parents_tree.clear()
m2m_changed.connect(tag_set_parents_tree, sender=Tag.parents_direct.through)