Django manual migration to add group - django

Question

I am attempting to create a migration that will automatically add a group and permissions to the group when it is run. I adapted some code from the docs and an example. I can get the migration to add the group but not the permissions. I am getting the following error: TypeError: Direct assignment to the forward side of a many-to-many set is prohibited. Use permissions.set() instead.
I am not sure how to implement this suggestion. Any ideas?
The migration:
from django.db import migrations, models
from django.contrib.auth.models import Group, Permission
from django.contrib.auth.management import create_permissions
def add_group_permissions(apps, schema_editor):
for app_config in apps.get_app_configs():
create_permissions(app_config, apps=apps, verbosity=0)
# Employee
group, created = Group.objects.get_or_create(name='Employee')
if created:
permissions_qs = Permission.objects.filter(
codename__in=[
'can_add_how_to_entry',
'can_change_how_to_entry',
'can_view_how_to_entry',
]
)
group.permissions = permissions_qs
group.save()
class Migration(migrations.Migration):
dependencies = [
('accounts', '0001_initial'),
]
operations = [
migrations.RunPython(add_group_permissions),
]

Answer 1

Remember that group.permissions is a related query manager, not a field, so if you assign something to that you will destroy it. So you need to do something like:
permissions_qs = Permission.objects ...
for permission in permissions_qs:
group.permissions.add(permission)
group.save()
Additionally, the Django way to create custom permission is through the Meta class, for example:
# Assuming that you have an "Entry" model
class Entry(models.Model):
...
class Meta:
...
permissions = [
('custom_permission_a', 'a description for permission a'),
('custom_permission_b', 'a description for permission b'),
]
After migrating the changes you will have two additional permissions attached to the Entry model.
Now you can create a group with the custom permissions like:
group, created = Group.objects.get_or_create(name='CustomGroup')
if created:
permissions = Permission.objects.filter(
codename__in=[
'custom_permission_a',
'custom_permission_b',
]
)
for p in permissions:
group.permissions.add(p)
group.save()
You can include that in a new migration or whatever you want, also if you don't want to use the Meta class to create your custom permissions, you can do it programmatically:
# Assuming that you have an Entry model
# Import Entry model
from django.contrib.auth.models import Permission
from django.contrib.contenttypes.models import ContentType
entryContentType = ContentType.objects.get_for_model(Entry)
# Create custom permission
custom_permission = Permission.objects.create(
codename ='custom_permission',
name ='description for the custom permission',
content_type = entryContentType
)
A custom_permission will be created and attached to the Entry model. Then you can include that permission in your custom group.