While I was waiting for suggestions, I did some more research learnt about django Conditional Expressions.
Docs: https://docs.djangoproject.com/en/1.9/ref/models/conditional-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())) Posting it here.. someone else may find it helpful. On Friday, 22 July 2016 22:02:09 UTC+1, mishbah wrote: > > You are awesome! Thank you! > > On Friday, 22 July 2016 21:41:58 UTC+1, Todor Velichkov wrote: >> >> 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 >>> >> -- You received this message because you are subscribed to the Google Groups "Django users" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/django-users. To view this discussion on the web visit https://groups.google.com/d/msgid/django-users/9573f60e-08e0-4c4b-a8e4-0fd7453cfb8a%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
