Well,
MAX_CUISINES = 3
def clean(self):
# three cuisines max. allowed
if self.pk is None:
# That's the case that raise the error
# you're inserting a new Restaurant
pass
else:
# Here, you're editing an existing Restaurant
# (including its relashionship with Cuisine)
if self.cuisines.count() > MAX_CUISINES:
raise ValidationError('I said, "Choose up to three"
cusines!')
As we're aiming to prevent, at model's level, saving a new Restaurant
when too many related Cuisine are provided, I'm afraid that doesn't fit
the needs... unless saving restaurant's intance, run a validation then
delete it if it fails the validation :) I'd like to place the validation
at 'cusines' field level. I'm not confortable placing it at the "whole"
model's level, despite my suggestion.
I failed for the moment to find a way and I'll resume tomorrow. Maybe
the following unsuccessful tries can help you (with a mix of admin
interface playing and shell, both on dev server):
* use validator on models.ManyToManyField:
I can't even trigger a simple print('test') TT
* use a custom field by extending models.ManyToManyField, overriding
its isValidIDList method
Ok, it is a blind test: I was looking for a way to access values
from cuisines for a non saved instance of Restaurant and maybe something
is lurking there. I'm a beginner.
* accessing self's attributes for a non saved or retrieved instance
of Restaurant
# desesperately random commands (I tried more :):
u = Restaurant()
r = Restaurant.objects.all()[0]
dir(u)
# hey, a "cuisines" attribute, great!
dir(u.cuisines)
# TT, same error you encountered
dir(r.cuisines)
# fine
u.clean_fields()
# 'cusines' is not even mentionned in the error message
r.clean_fields()
# fine
[f.verbose_name for f in r._meta.fields]
# no cusines
I believe that no control is enforced before saving, but if you
try to create an new Restaurant and not provide a cuisine, the
validation failed from the admin. How does it handle that? I'll try to
find out. Is there a way to access data provided to 'cuisines' for an
unsaved Restaurant?
Regards,
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