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Django: How to delete a group which is related to a team?

I want to extend Django's group model. To do so I've created a Team class, which references the group model with a OneToOne field. Create and update work as expected, but I fail to delete the team.
# teamapp/models.py
from django.db import models
from rules.contrib.models import RulesModel
from django.contrib.auth.models import Group
class Team(RulesModel):
group = models.OneToOneField(
Group,
on_delete=models.CASCADE,
primary_key=True,
)
name = models.CharField(max_length=80)
def save(self, *args, **kwargs):
self.update_or_create_group()
return super().save(*args, **kwargs)
def update_or_create_group(self, *args, **kwargs):
team_group, _ = Group.objects.update_or_create(
id=self.pk,
defaults={"name": self.name},
)
self.group = team_group
# teamapp/signals.py
from django.db.models.signals import post_delete
from django.dispatch import receiver
from django.db import transaction
from django.contrib.auth.models import Group
from teamapp.models import Team
#receiver(post_delete, sender=Team)
def delete_group(sender, instance, **kwargs):
# TODO: Use celery for async operation: https://docs.djangoproject.com/en/3.2/topics/db/transactions/
transaction.on_commit(lambda: delete_group(instance))
def delete_group(team_instance):
Group.objects.filter(id=team_instance.group.id).delete()
Somehow the signal doesn't trigger. Is there an other way?

Not sure if this is an acceptable way, but I forgot to load the signal. So I've loaded it though the apps.py file.
# teamapp/apps.py
from django.apps import AppConfig
class TeamappConfig(AppConfig):
default_auto_field = "django.db.models.BigAutoField"
name = "teamapp"
verbose_name = "Team"
def ready(self):
import teamapp.signals

Django FileField not respecting null=False parameter

I have a Django FileField which is set to not nullable. However it is behaving like it is nullable.
class Thing(models.Model):
document = models.FileField(null=False, blank=False)
thing_id = models.CharField()
# This does not raise but I would like it to
Thing.objects.create(thing_id='123')
edit: the migrations
class Migration(migrations.Migration):
dependencies = [
('data_source', '0002_auto_20190212_1913'),
]
operations = [
migrations.CreateModel(
name='Thing',
fields=[
('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
('document', models.FileField(upload_to='')),
('thing_id', models.CharField(default=None, max_length=200)),
],
options={
'abstract': False,
},
),
]

The problem is not with your field definition. It's got to do with validation when manually creating a model instance. You need to perform that full validation yourself, since you're not using a ModelForm.
Use this example:
from django.core.exceptions import ValidationError
thing = Thing(thing_id='123')
try:
thing.full_clean()
thing.save()
except ValidationError:
# Handle validation issues.
Read this section in the documentation: https://docs.djangoproject.com/en/2.1/ref/models/instances/#validating-objects
Quoting from there:
Note that full_clean() will not be called automatically when you call
your model’s save() method. You’ll need to call it manually when you
want to run one-step model validation for your own manually created
models

You can add the validation directly in your model overriding save() method:
class Thing(models.Model):
document = models.FileField(null=False, blank=False, default=None)
thing_id = models.CharField(max_length=200)
def save(self, *args, **kwargs):
self.full_clean()
super().save(*args, **kwargs)

By default null and blank are False. Link for every model field. Don't need to add those.
from django.db import models
class Thing(models.Model):
document = models.FileField()
thing_id = models.CharField()

Django fixtures save with default value

I'm using Django 1.7 and I have a problem with my fixtures.
I would like Django to use the default value or use the save() method to create unspecified values.
Here are my current objects:
# File: uuidable.py
import uuid
from django.db import models
from django.utils.translation import ugettext_lazy as _
class Uuidable(models.Model):
uuid = models.CharField(_('uuid'), blank=True,
null=False, unique=True,
max_length=64, default=uuid.uuid4()) # Tried here
class Meta:
abstract = True
def save(self, *args, **kwargs):
if self.pk is None:
self.uuid = uuid.uuid4() # Tried here also
super().save(*args, **kwargs)
# File: timestampable.py
from django.db import models
from django.utils.translation import ugettext_lazy as _
class Timestampable(models.Model):
created_at = models.DateTimeField(_('created at'), auto_now_add=True)
updated_at = models.DateTimeField(_('updated at'), auto_now=True)
class Meta:
abstract = True
# File: post.py
from project.lib.models.timestampable import Timestampable
from project.lib.models.uuidable import Uuidable
class Post(Timestampable, Uuidable):
title = models.CharField(_('title'), max_length=250, blank=False)
content = models.TextField(_('content'))
def __str__(self):
return self.title
As you can see, when I generate a new Post(), the created_at, updated_at and uuid values are automatically created on save(). But when I use fixtures, I get the following error:
[...]initial_data.yaml': Could not load post.Post(pk=None): UNIQUE constraint failed: post_post.uuid
If I specify a uuid in my fixture file, then I get an error on created_at and then on updated_at. So I have to specify the content of each field, even though I want it to be "automatic".
From the documentation (why is this in the django admin docs ?!), I know that the save() method is not called so this is why everything I put into the save() method doesn't work. But shouldn't the default or auto_now* features be enables/used ?
When fixture files are processed, the data is saved to the database as is. Model defined save() methods are not called, and any pre_save or post_save signals will be called with raw=True since the instance only contains attributes that are local to the model. You may, for example, want to disable handlers that access related fields that aren’t present during fixture loading and would otherwise raise an exception
Is there a way to "force" Django to automatically use the default or auto_now* features for fixtures ? I'm using manage.py syncdb to create all the tables etc.
I have searched on google and stack overflow but couldn't seem to find the right search keywords.
UPDATE-1: The following google group discussion says that objects are saved in raw mode, meaning that auto_now* features are not taken into account. I'm still searching to see if there is a way to hook some model function to the Django fixture saving.

The solution was to use django signals:
import uuid
from django.db import models
from django.utils.translation import ugettext_lazy as _
from django.db.models.signals import pre_save
from django.dispatch import receiver
class Uuidable(models.Model):
uuid = models.CharField(_('uuid'), blank=True,
null=False, unique=True,
max_length=64, default=uuid.uuid4())
class Meta:
abstract = True
#receiver(pre_save)
def set_uuid_on_save(sender, instance, *args, **kwargs):
if instance.pk is None:
instance.uuid = uuid.uuid4()
That way, the model/data is populated whatever way you create the model (via shell, fixtures, whatever).

Automatically loading initial data fixtures is deprecated in Django 1.7. One solution is via signals as you mentioned.
Another one that I prefer is to create a python script where you create all the needed data, and execute it in the shell:
python manage.py shell < create_initial_data.py

I think that the problem is when you put default=uuid.uuid4(). The parenthesis are too much, because they imply that you pass the result of uuid.uuid4() to default argument and not the function itself, so you should put default=uuid.uuid4.

Django: MultiValueField and MultiWidget

Django's documentation doesn't do a very thorough job of explaining how to use MultiValueField and MultiWidget. I've tried dissecting the one implementation and haven't had good results. Would someone mind giving me a quick pointer in the right direction?
My example:
widgets.py
from django import forms
class TestMultiWidget(forms.MultiWidget):
def __init__(self, attrs=None):
widgets = (
forms.TextInput(attrs=attrs),
forms.TextInput(attrs=attrs),
)
super(TestMultiWidget, self).__init__(widgets, attrs)
def decompress(self, value):
if value:
return value.split(':::')[0:2]
return ['', '']
fields.py
from django import forms
from widgets import TestMultiWidget
class TestMultiField(forms.MultiValueField):
widget = TestMultiWidget
def __init__(self, *args, **kwargs):
fields = (
forms.CharField(),
forms.CharField(),
)
super(TestMultiField, self).__init__(fields, *args, **kwargs)
def compress(self, data_list):
if data_list:
return ':::'.join(data_list)
return ''
models.py
from django.db import models
from util.fields import TestMultiField
class Test(models.Model):
a = models.CharField(max_length=128)
b = TestMultiField()
c = models.CharField(max_length=128)
admin.py
from django.contrib import admin
from models import Test
admin.site.register(Test)
And the resulting admin.
Anybody have a clue what's happening here? My guess is that there's some unintended exception suppression happening, but I haven't been able to locate the source.
Thanks!

Please notice that django.forms.MultiValueField is a form field and not a model field (like django.db.models.CharField). Therefore, it is not treated as a model field in your Test model, and was not created in your database. (You can check it with ./manage.py sqlall myapp).
Change your models.py to:
from django.db import models
from fields import TestMultiField
class TestMultiModelField(models.Field):
def formfield(self, **kwargs):
defaults = {'form_class': TestMultiField}
defaults.update(kwargs)
return super(TestMultiModelField, self).formfield(**defaults)
def get_internal_type(self):
return 'TextField'
class Test(models.Model):
a = models.CharField(max_length=128)
b = TestMultiModelField()
c = models.CharField(max_length=128)
drop your table (on linux/mac: ./manage.py sqlclear myapp | ./manage.py dbshell) and syncdb to create your table, this time with column b. Check your admin now.
Explanation:
To create a custom model field, follow this: https://docs.djangoproject.com/en/dev/howto/custom-model-fields/
The set the model field's matching form field, the formfield method was used.
(BTW, The "correct" way to design the model field is probably a bit different, using to_python and get_prep_value)

How do I extend the Django Group model?

Is there a way to extend the built-in Django Group object to add additional attributes similar to the way you can extend a user object? With a user object, you can do the following:
class UserProfile(models.Model):
user = models.OneToOneField(User)
and add the following to the settings.py file
AUTH_PROFILE_MODULE = 'app.UserProfile'
which gets you:
profile = User.objects.get(id=1).get_profile()
Is there any equivalent to this approach for extending a group? If not, is there an alternative approach I can take?

If you simply subclass the Group object then by default it will create a new database table and the admin site won't pick up any new fields.
You need to inject new fields into the existing Group:
if not hasattr(Group, 'parent'):
field = models.ForeignKey(Group, blank=True, null=True, related_name='children')
field.contribute_to_class(Group, 'parent')
To add methods to the Group, subclass but tag the model as proxy:
class MyGroup(Group):
class Meta:
proxy = True
def myFunction(self):
return True

You can create a model that subclasses Group, add your own fields, and use a Model Manager to return any custom querysets you need. Here's a truncated example showing how I extended Group to represent Families associated with a school:
from django.contrib.auth.models import Group, User
class FamilyManager(models.Manager):
"""
Lets us do querysets limited to families that have
currently enrolled students, e.g.:
Family.has_students.all()
"""
def get_query_set(self):
return super(FamilyManager, self).get_query_set().filter(student__enrolled=True).distinct()
class Family(Group):
notes = models.TextField(blank=True)
# Two managers for this model - the first is default
# (so all families appear in the admin).
# The second is only invoked when we call
# Family.has_students.all()
objects = models.Manager()
has_students = FamilyManager()
class Meta:
verbose_name_plural = "Families"
ordering = ['name']
def __unicode__(self):
return self.name

I managed to use migrations with #Semprini aswer.
So i needed to create a company related field in my groups related field, so in my models i did this:
if not hasattr(Group, 'company'):
field = models.ForeignKey(Company, on_delete=models.DO_NOTHING, null=True)
field.contribute_to_class(Group, 'company')
class Group(Group):
class Meta:
proxy = True
Then i run manage.py makemigrations. This created 2 files. One with dependencies on the other, but the first one belonging to the auth app was created inside my virtual enviroment. The files look like this:
# Generated by Django 2.2.5 on 2019-10-08 16:00
from django.db import migrations, models
import django.db.models.deletion
class Migration(migrations.Migration):
dependencies = [
('myapp', '0013_guestuser_permissions_20190919_1715'),
('auth', '0011_update_proxy_permissions'),
]
operations = [
migrations.AddField(
model_name='group',
name='company',
field=models.ForeignKey(
null=True, on_delete=django.db.models.deletion.DO_NOTHING, to='myapp.Company'),
),
]
The second one created in myapp migrations folder look like this:
# Generated by Django 2.2.5 on 2019-10-08 16:00
import django.contrib.auth.models
from django.db import migrations
class Migration(migrations.Migration):
dependencies = [
('auth', '0012_group_company_20191008'),
('myapp', '0013_guestuser_permissions_20190919_1715'),
]
operations = [
migrations.CreateModel(
name='Group',
fields=[
],
options={
'proxy': True,
'indexes': [],
'constraints': [],
},
bases=('auth.group',),
managers=[
('objects', django.contrib.auth.models.GroupManager()),
],
),
]
So the solution was to move the file created in my virtualenv to myapp migrations folder, before the other one generated with makemigrations, but since the migration is applied to the auth app instead of myapp i have to implement a workaround in the file. So the final file now is:
# Generated by Django 2.2.5 on 2019-10-08 16:00
from django.db import migrations, models
import django.db.models.deletion
class Migration(migrations.Migration):
dependencies = [
('myapp', '0013_guestuser_permissions_20190919_1715'),
('auth', '0011_update_proxy_permissions'),
]
operations = [
migrations.AddField(
model_name='group',
name='company',
field=models.ForeignKey(
null=True, on_delete=django.db.models.deletion.DO_NOTHING, to='myapp.Company'),
),
]
def mutate_state(self, project_state, preserve=True):
"""
This is a workaround that allows to store ``auth``
migration outside the directory it should be stored.
"""
app_label = self.app_label
self.app_label = 'auth'
state = super(Migration, self).mutate_state(project_state, preserve)
self.app_label = app_label
return state
def apply(self, project_state, schema_editor, collect_sql=False):
"""
Same workaround as described in ``mutate_state`` method.
"""
app_label = self.app_label
self.app_label = 'auth'
state = super(Migration, self).apply(project_state, schema_editor, collect_sql)
self.app_label = app_label
return state
The mutate an apply methods allow you to migrate to the auth app from myapp migrations.
In the second file i just change the dependencie to depend on the newly file created:
# Generated by Django 2.2.5 on 2019-10-08 16:00
import django.contrib.auth.models
from django.db import migrations
class Migration(migrations.Migration):
dependencies = [
('myapp', '0014_group_company_20191008'),
('myapp', '0013_guestuser_permissions_20190919_1715'),
]
operations = [
migrations.CreateModel(
name='Group',
fields=[
],
options={
'proxy': True,
'indexes': [],
'constraints': [],
},
bases=('auth.group',),
managers=[
('objects', django.contrib.auth.models.GroupManager()),
],
),
]

For me worked solution based on:
https://docs.djangoproject.com/pl/1.11/topics/auth/customizing/#extending-user
Let me explain what I did with Groups extending default model with email alias:
First of all I created my own django application let name it
python manage.py startapp auth_custom
Code section:
In auth_custom/models.py I created object CustomGroup
from django.contrib.auth.models import Group
from django.db import models
class CustomGroup(models.Model):
"""
Overwrites original Django Group.
"""
def __str__(self):
return "{}".format(self.group.name)
group = models.OneToOneField('auth.Group', unique=True)
email_alias = models.EmailField(max_length=70, blank=True, default="")
In auth_custom/admin.py:
from django.contrib.auth.admin import GroupAdmin as BaseGroupAdmin
from django.contrib.auth.models import Group
class GroupInline(admin.StackedInline):
model = CustomGroup
can_delete = False
verbose_name_plural = 'custom groups'
class GroupAdmin(BaseGroupAdmin):
inlines = (GroupInline, )
# Re-register GroupAdmin
admin.site.unregister(Group)
admin.site.register(Group, GroupAdmin)
After making migrations I have such result in Django Admin view.
Custom Group in Django Admin
In order to access this custom field you must type:
from django.contrib.auth.models import Group
group = Group.objects.get(name="Admins") # example name
email_alias = group.customgroup.email_alias
If any mistakes please notify me, I'll correct this answere.