def _get_not_null_pk(self, field, using):
# XXX the below logic is required to get the expected results back
# when querying for NULL values. since NULL can be a value and a
# placeholder for non-existent values, then a condition to ensure
# the row's primary key is also NOT NULL must be added. Django
# assumes in all cases when querying on a NULL value all joins in
# the chain up to that point must be promoted to LEFT OUTER JOINs,
# which could be a reasonable assumption for some cases, but for
# getting the existent rows of data back for our purposes, the
# assumption is wrong.
# if this field is already the primary key, then don't bother
# adding the test, since it would be redundant
if field.field.primary_key:
return Q()
from avocado.models import Field
pk_name = field.model._meta.pk.name
pk_field = Field(app_name=field.app_name,
model_name=field.model_name, field_name=pk_name)
key = pk_field.query_string('isnull', using=using)
return Q(**{key: False})
