Signals in Django - django

Question

I have 2 models.py files in different app directories: users.models.py and friends.models.py.
There is one problem: if some user deleted from UserProfile model, all his friendship network must be deleted too with him. It is very natural.
But when I import Frienship to users.model.py I've got an error: Cannot import name Friendship
I understand an error arose because of mutual importing in these 2 files, and I know I can easely solve this problem with the help of signals, but I do not know how to do it in proper way.
Could anybody help in this particular case?
In users.models.py:
from friends.models import Friendship
class UserProfile(models.Model):
username = models.Charfield(max_length=50)
...
def delete(self, *args, **kwargs):
Friendship.objects.remove_all(self)
self.delete(*args, **kwargs)
In friends.models.py:
from users.models import UserProfile
class FriendshipManager(models.Manager):
def remove_all(self, user):
usr = Friendship.objects.get(user=user).friends
frs = [i.user for i in usr.all()]
for fr in frs:
usr.remove(fr)
class Friendship(models.Model):
user = models.Foreignkey(UserProfile)
friends = models.ManyToManyField('self')
objects = FriendshipManager()
Thanks in advance!!!

Answer 1

No need for signals, just use the magic *_set property. It will be defined at runtime so you don't have to worry about circular imports.
friends/models.py
from users.models import UserProfile
class Friendship(models.Model):
user = models.Foreignkey(UserProfile)
friends = models.ManyToManyField('self')
users/models.py
class UserProfile(models.Model):
username = models.Charfield(max_length=50)
...
def delete(self, *args, **kwargs):
for f in self.friendship_set.all():
f.delete()
super(self.__class__, self).delete(*args, **kwargs)

Answer 2

This is what I usually do, you could easily refactor this to implement with your model
from django.db import models
from django.db.models.signals import post_save, post_delete
from django.contrib.auth.models import User
# App specific
class UserProfile(models.Model):
"""
Adds a basic UserProfile for each User on the fly.
"""
user = models.OneToOneField(User)
avatar = models.ImageField(upload_to='example/somewhere', blank=True)
def __str__(self):
return "%s's profile" % self.user
def get_avatar(self):
return '/'+self.avatar
def clean_avatar(self):
# TODO: imagekit
pass
class Meta:
app_label = 'users'
def save(self, *args, **kwargs):
if self.id:
this = UserProfile.objects.get(id=self.id)
if this.avatar:
if this.avatar != self.avatar:
this.avatar.delete(save=False)
super(UserProfile, self).save()
def create_user_profile(sender, instance, created, **kwargs):
if created:
profile, created = UserProfile.objects.get_or_create(user=instance)
post_save.connect(create_user_profile, sender=User)
def UserProfileDelete(instance, **kwargs):
"""
Documentatie
"""
instance.avatar.delete(save=False)
post_delete.connect(UserProfileDelete, sender=UserProfile)