How to access both directions of ManyToManyField in Django Admin?

Question

The Django admin filter_horizontal setting gives a nice widget for editing a many-to-many relation. But it\'s a special setting that wants a list of fields, so it\'

Answer 1

Here's a (more or less) tidy solution, thanks to http://blog.abiss.gr/mgogoulos/entry/many_to_many_relationships_and and with a fix for a Django bug taken from http://code.djangoproject.com/ticket/5247

from django.contrib import admin as admin_module

class SiteForm(ModelForm):
    user_profiles = forms.ModelMultipleChoiceField(
        label='Users granted access',
        queryset=UserProfile.objects.all(),
        required=False,
        help_text='Admin users (who can access everything) not listed separately',
        widget=admin_module.widgets.FilteredSelectMultiple('user profiles', False))

class SiteAdmin(admin_module.ModelAdmin):
    fields = ('user_profiles',)

    def save_model(self, request, obj, form, change):
        # save without m2m field (can't save them until obj has id)
        super(SiteAdmin, self).save_model(request, obj, form, change) 
        # if that worked, deal with m2m field
        obj.user_profiles.clear()
        for user_profile in form.cleaned_data['user_profiles']:
             obj.user_profiles.add(user_profile)

    def get_form(self, request, obj=None, **kwargs):
        if obj:
            self.form.base_fields['user_profiles'].initial = [ o.pk for o in obj.userprofile_set.all() ]
        else:
            self.form.base_fields['user_profiles'].initial = []
        return super(SiteAdmin, self).get_form(request, obj, **kwargs)

This uses the same widget as the filter_horizontal setting, but hard-coded into the form.