Easy custom media and validation in newforms-admin

[mrts]

Attaching media (especially JavaScript) and custom validation is a common use case for admin section. It should be easy.

As of [7278], get_form() can be used to provide a custom form that can bring in JavaScript and custom validation. Due to bugs, once this method is overriden, your form will not automatically get the custom admin widgets. As the automatic widgets are the main point of using admin, this is not generally acceptable.

The proposed behaviour (that is implemented in the attached patch -- thanks, Brosner, for the bug fix!) is as follows:

# A Foo with unique language
class Foo(models.Model):
    foo = models.TextField()
    language = models.CharField(max_length=3, choices=LANG_CHOICES, unique=True)
    def __unicode__(self):
        return 'Foo in %s' % self.get_language_display()

# common base class for attaching TinyMCE to several validator forms
class TinyMCEForm(forms.ModelForm):
    media = forms.Media(
        js = ['/site_media/js/tiny_mce/tiny_mce.js',
                '/site_media/js/add_editor.js'])

# a common validator form for all models with a 'language' field
class LanguageValidatorForm(TinyMCEForm):
    def clean_language(self):
        if 'language' not in self.cleaned_data:
            return
        lang = self.cleaned_data['language']
        model = self._meta.model
        if model.objects.filter(language = lang).exclude(pk=self.instance.pk):
            raise forms.ValidationError('%(obj_title)s already exists for '
                    'language %(lang)s. Only one %(obj)s is allowed for '
                    'each language.'
                    % { 'obj_title' : model._meta.verbose_name.title(),
                        'obj' : model._meta.verbose_name,
                        'lang' : admin_forms.get_lang_display(lang)})

class LanguageAdmin(admin.ModelAdmin):
    admin_form = LanguageValidatorForm
    save_on_top = True

admin.site.register(Foo, LanguageAdmin)

I.e. there is a class variable that specifies the form that brings in both validation and media.

[mrts]

Implementation of the proposal.

[mrts]

Fixes inline forms as well.

[mrts]

I was over-enthusiastic, the patch does not fix the widget breakage problem.

[mrts]

Use BaseModelForm throughout, accept it as a parent in ModelFormMetaclass

[Brian Rosner]

(In [7360]) newforms-admin: Fixed #6866 -- ModelAdmin.get_form and InlineModelAdmin.get_formset now uses BaseModelAdmin.form so the form class can be changed out very easily.

[Brian Rosner]

It is a tad too late, but I did forget to thank mrts for his work on this. So, thanks, mrts. :)