Hello, I don't think sub-classing `Func` would be appropriate here. A much
easier way would be to use `RawSQL
<https://docs.djangoproject.com/en/1.8/ref/models/expressions/#raw-sql-expressions>
`
since you want to dynamically check for different group you could write a
factory method to build `RawSQLs` for you, something like:
from django.db.models import BooleanField
from django.db.models.expressions import RawSQL
def build_has_group_raw_sql(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())
Now you can use this function as follows:
User.objects.all().annotate(is_customer=build_has_group_raw_sql('customer'))
On Friday, July 22, 2016 at 7:01:08 PM UTC+3, mishbah wrote:
>
> 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
>
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