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 18441 A ModelForm with a blank=True, null=False ForeignKey doesn't validate James Aylett nobody "For the following: {{{ class Collection(models.Model): created_by = models.ForeignKey(User, null=False, blank=True) # and some other fields }}} (with a pre_save hook that populates `created_by` if it isn't already set), if on creation in the admin the HTML input for `created_by` is left empty (raw id) or unselected (non-raw id ie dropdown of all users), Django will attempt to set the field to `None`, which will result in a field validation failure: {{{ File ""/home/james/projects/artfinder/ENV/lib/python2.6/site-packages/django/core/handlers/base.py"" in get_response 111. response = callback(request, *callback_args, **callback_kwargs) File ""/home/james/projects/artfinder/ENV/lib/python2.6/site-packages/django/contrib/admin/options.py"" in wrapper 366. return self.admin_site.admin_view(view)(*args, **kwargs) File ""/home/james/projects/artfinder/ENV/lib/python2.6/site-packages/django/utils/decorators.py"" in _wrapped_view 91. response = view_func(request, *args, **kwargs) File ""/home/james/projects/artfinder/ENV/lib/python2.6/site-packages/django/views/decorators/cache.py"" in _wrapped_view_func 89. response = view_func(request, *args, **kwargs) File ""/home/james/projects/artfinder/ENV/lib/python2.6/site-packages/django/contrib/admin/sites.py"" in inner 196. return view(request, *args, **kwargs) File ""/home/james/projects/artfinder/ENV/lib/python2.6/site-packages/django/utils/decorators.py"" in _wrapper 25. return bound_func(*args, **kwargs) File ""/home/james/projects/artfinder/ENV/lib/python2.6/site-packages/django/utils/decorators.py"" in _wrapped_view 91. response = view_func(request, *args, **kwargs) File ""/home/james/projects/artfinder/ENV/lib/python2.6/site-packages/django/utils/decorators.py"" in bound_func 21. return func(self, *args2, **kwargs2) File ""/home/james/projects/artfinder/ENV/lib/python2.6/site-packages/django/db/transaction.py"" in inner 209. return func(*args, **kwargs) File ""/home/james/projects/artfinder/ENV/lib/python2.6/site-packages/django/contrib/admin/options.py"" in add_view 937. if form.is_valid(): File ""/home/james/projects/artfinder/ENV/lib/python2.6/site-packages/django/forms/forms.py"" in is_valid 124. return self.is_bound and not bool(self.errors) File ""/home/james/projects/artfinder/ENV/lib/python2.6/site-packages/django/forms/forms.py"" in _get_errors 115. self.full_clean() File ""/home/james/projects/artfinder/ENV/lib/python2.6/site-packages/django/forms/forms.py"" in full_clean 272. self._post_clean() File ""/home/james/projects/artfinder/ENV/lib/python2.6/site-packages/django/forms/models.py"" in _post_clean 309. self.instance = construct_instance(self, self.instance, opts.fields, opts.exclude) File ""/home/james/projects/artfinder/ENV/lib/python2.6/site-packages/django/forms/models.py"" in construct_instance 51. f.save_form_data(instance, cleaned_data[f.name]) File ""/home/james/projects/artfinder/ENV/lib/python2.6/site-packages/django/db/models/fields/__init__.py"" in save_form_data 454. setattr(instance, self.name, data) File ""/home/james/projects/artfinder/ENV/lib/python2.6/site-packages/django/db/models/fields/related.py"" in __set__ 362. (instance._meta.object_name, self.field.name)) Exception Type: ValueError at /admin/galleries/collection/add/ Exception Value: Cannot assign None: ""Collection.created_by"" does not allow null values. }}} I would expect this not to happen, allowing the presave hook to step in and do the right thing. If there's an obvious solution that I just haven't noticed, or no solution, then the rest of this can be skipped. I believe that the following note in `BaseModelForm._get_validation_exclusions()` explains what's going on: Note: don't exclude the field from validation if the model field allows blanks. If it does, the blank value may be included in a unique check, so cannot be excluded from validation. However I cannot find anything in the documentation that would suggest this behaviour. The current suggested solution, I think, would be to have the field explicitly listed in the `ModelForm` subclass **and** in `excludes` in that form. That would be something like: {{{ class CollectionAdminForm(forms.ModelForm): # need to exclude created_by, but explicitly list it as a field created_by = # SOMETHING class Meta: model = Collection exclude = ('created_by',) }}} however there's nothing in the documentation to suggest what the SOMETHING should be (ie what form field type should be used for `created_by`). If I try to use a `ModelChoiceField`, it doesn't populate it from the instance we're editing. Worse, because I'm linking to `User` I really want this to be a raw id field, and that seems to be utterly magical and doesn't have an actual form field type to represent it. At this point I think I've convinced myself that Django cannot do what I want, ie there's no simple way of configuring the admin to allow a presave-populated `ForeignKey` to be settable on creation but to fall back to the presave population." Bug closed Forms 1.4 Normal duplicate Accepted 0 0 0 0 0 0