__init__.py 文件源码

def _check_null_allowed_for_primary_keys(self):
        if (self.primary_key and self.null and
                not connection.features.interprets_empty_strings_as_nulls):
            # We cannot reliably check this for backends like Oracle which
            # consider NULL and '' to be equal (and thus set up
            # character-based fields a little differently).
            return [
                checks.Error(
                    'Primary keys must not have null=True.',
                    hint=('Set null=False on the field, or '
                          'remove primary_key=True argument.'),
                    obj=self,
                    id='fields.E007',
                )
            ]
        else:
            return []