Django: filtering queryset by 'field__isnull=True' or 'field=None'?

django django-models django-queryset isnull
Don picture Don · May 3, 2013 · Viewed 31.1k times · Source

I have to filter a queryset by a dynamic value (which can be None): may I simply write:

filtered_queryset = queryset.filter(field=value)

or shall I check for None:

if value is None:
    filtered_queryset = queryset.filter(field__isnull=True)
else:
    filtered_queryset = queryset.filter(field=value)

Does the behaviour depend on the particular DBMS?

Answer

Hedde van der Heide picture Hedde van der Heide · May 3, 2013

The ORM will handle None (cast it to NULL) for you and return a QuerySet object, so unless you need to catch None input the first example is fine.

>>> User.objects.filter(username=None)
[]
>>> type(_)
<class 'django.db.models.query.QuerySet'>
>>> str(User.objects.filter(username=None).query)
SELECT "auth_user"."id", "auth_user"."username", "auth_user"."first_name", "auth_user"."last_name", "auth_user"."email", "auth_user"."password", "auth_user"."is_staff", "auth_user"."is_active", "auth_user"."is_superuser", "auth_user"."last_login", "auth_user"."date_joined" FROM "auth_user" WHERE "auth_user"."username" IS NULL

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