id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
15323	django.db.models.Model.clean() should be independent from .clean_fields()	Tim Molendijk	nobody	"From http://code.djangoproject.com/browser/django/trunk/django/db/models/base.py#L811:

{{{
# Form.clean() is run even if other validation fails, so do the
# same with Model.clean() for consistency.
}}}

This behavior can be surprisingly annoying. Assume a model {{{Car}}} with a foreign key field ({{{null=False}}}) named {{{owner}}}. Now assume one of the restrictions on {{{Car}}} is that {{{owner.gender == 'm'}}} (yeah ridiculous, I know ;)). One would think that a model clean method as follows would do the job:

{{{
def clean(self):
    if self.owner.gender != 'm':
        raise ValidationError(""Women are not allowed to own cars!"")
}}}

BUT, this will crash the system every time you try to save a car instance that has no owner assigned. One would say that {{{clean()}}} does not have to worry about the requirement that an owner is obligatory, because that's what {{{clean_fields()}}} is for, right? WRONG, because {{{clean()}}} will always run, regardless of the success of {{{clean_fields()}}}. And running {{{clean()}}} will result in an {{{ObjectDoesNotExist}}} error because {{{self.owner}}} does not have a value.

The consequence is that {{{clean()}}} must anticipate on '''all''' potential validation errors in {{{clean_fields()}}}. Bye bye separation of concerns..."		closed	Database layer (models, ORM)	dev		invalid	model validation clean		Unreviewed	0	0	0	0	0	0