Annotate django user queryset with group names

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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