Annotate django user queryset with group names - django

Question

Given that I have a django model that has a ForeignKey that is linked to itself.
class DjangoModel():
[...]
successor = models.ForeignKey('self', null=True)
I was able to write a custom django database function like this:
from django.db.models import BooleanField
from django.db.models import Func
class IsNull(Func):
"""
See docs: https://docs.djangoproject.com/en/1.8/ref/models/database-functions/
"""
template = '%(expressions)s IS NULL'
def __init__(self, *args, **kwargs):
kwargs['output_field'] = BooleanField()
super(IsNull, self).__init__(*args, **kwargs)
So I can do this:
queryset = DjangoModel.objects.all()
queryset = queryset.annotate(**{'is_latest': IsNull('successor')})
and if use queryset.values() .. I get
[{'pk': 1, is_latest': True}, {'pk': 2, 'is_latest': False}, ]
where is_latest == True when successor field is NULL for an object.
Now I want to do something similar, but have no idea where to start!
The bundled django.contrib.auth.models.User has a ManyToMany relations to django.contrib.auth.models.Group model
For my project, there are multiple user group types, e.g customer / marketing / finance etc
What I want to do.. is annotate a User queryset with is_FOO field where FOO is a group name. e.g is_customer or is_marketing
So if I use .values() on a queryset, I should get something like this:
[{'pk': 1, 'is_customer': True, 'is_marketing': False }, {'pk': 1, 'is_customer': True, 'is_marketing': True }]
The group name could be hardcoded, e.g
queryset.annotate(**{'is_customer': IsGroupMember('customer')})
I just need help with the IsGroupMember database function!
Is that even possible? Any hints or tips to get me started?
Any help will be genuinely appreciated. Many Thanks

Answer 1

I have 2 solutions for the problem :-)
Given that I'm using the django auth user model
from django.contrib.auth.models import User
and the group name I'm interested in:
CUSTOMER_GROUP_NAME = 'customer'
Solution 1 — as suggested by Todor Velichkov in django-users google group.
Slightly modified version of his answer below:
from django.db.models.expressions import RawSQL
def is_group_member(group_name):
return RawSQL("""EXISTS(
SELECT 1 FROM `auth_group`
WHERE `auth_group`.`name` = %s
AND `auth_group`.`id` IN (
SELECT `auth_user_groups`.`group_id`
FROM `auth_user_groups`
WHERE `auth_user_groups`.`user_id` = `auth_user`.`id`
)
)""", (group_name,), output_field=BooleanField())
qs1 = User.objects.all().annotate(is_customer=is_group_member(CUSTOMER_GROUP_NAME))
Link to original answer: https://groups.google.com/d/msg/django-users/BLCGZtUzEcY/w5w87frbBgAJ
I did some more research and learnt about django conditional expressions.
Docs: https://docs.djangoproject.com/en/1.9/ref/models/conditional-expressions/
Solution 2 — using django expressions :-)
from django.contrib.auth.models import User
from django.db.models import BooleanField
from django.db.models import When, Case, Value
query = When(groups__name__in=[CUSTOMER_GROUP_NAME, ], then=Value(1))
qs2 = User.objects.annotate(
is_customer=Case(query, default=Value(0), output_field=BooleanField()))
I think "Solution 2" is cleaner and easier to read. So I'll be using that :-)