rewriting unfilled field of the model in Django

Question

I have a model of object Obj created in django with some fields (A,B,C) While creating some of the objects in data base people did not fill B field. Now I want to filter objects by B, like: for obj in all_Obj: if obj.B = "something": obj.delete()

But I am getting this error: users.models.DoesNotExist: Profile matching query does not exist for the line: if c.main_name.user == user[0]: The same error I am getting when writing if not c.main_name.user: So how can I solve this? I can not rewrite this field because I can not address it and I can not filter by this field to delete some entries I don't need

Thanks a lot for help.. :)

In the request c is concept:

class Concept(models.Model):
    partial_url = models.CharField(max_length=200, unique=True)
    insert_links = models.BooleanField(default=True)
    is_category = models.BooleanField(default=False)
    date_modified = models.DateTimeField(auto_now=True)
    main_name = models.ForeignKey('Literal', related_name='concepts', blank=True, null=True,
    unique=True)
    category = models.ForeignKey('self', blank=True, null=True)
deletion_requests = generic.GenericRelation(DeletionRequest,
        content_type_field='entry_ct', object_id_field='entry_id')

And c.main_name is Literal:

class Literal(models.Model):
    """Represents particular string literal of the concept"""
    name = models.CharField(max_length=200)
    norm_name = models.CharField(max_length=200)
    concept = models.ForeignKey(Concept)
    user = models.ForeignKey(Profile)
    date_modified = models.DateTimeField(auto_now=True)

Unexisting field - user

Answer 1

YourModel.objects.filter(B='something').delete()

or for empty foreign key:

YourModel.objects.filter(B__isnull=True).delete()