Adding a ManyToManyWidget to the reverse of a ManyToManyField in the Django Admin

Question

Let's say I have a simple blog app in Django 1.4:

class Post(models.Model):     title = …     published_on = …     tags = models.ManyToManyField('Tag')  class Tag(models.Model):     name = … 

i.e. a post has many tags. On the Django admin, I get a nice little <select multi> if I include tags in the fields for the PostAdmin. Is there an easy way to include the list of the posts (as a simple <select multi>) in the TagAdmin? I tried putting fields = ['name', 'posts'] in the TagAdmin and got an ImproperlyConfigured error. (same result for post_set).

I'm alright with Django, so could whip up a proper AdminForm and Admin object, but I'm hoping there a Right Way™ to do it.

Answer 1

This is possible to do with a custom form.

from django.contrib import admin from django import forms  from models import Post, Tag  class PostAdminForm(forms.ModelForm):     tags = forms.ModelMultipleChoiceField(         Tag.objects.all(),         widget=admin.widgets.FilteredSelectMultiple('Tags', False),         required=False,     )      def __init__(self, *args, **kwargs):         super(PostAdminForm, self).__init__(*args, **kwargs)         if self.instance.pk:             self.initial['tags'] = self.instance.tags.values_list('pk', flat=True)      def save(self, *args, **kwargs):         instance = super(PostAdminForm, self).save(*args, **kwargs)         if instance.pk:             instance.tags.clear()             instance.tags.add(*self.cleaned_data['tags'])         return instance  class PostAdmin(admin.ModelAdmin):     form = PostAdminForm  admin.site.register(Post, PostAdmin) 

That False in there can be replaced with a True if you want vertically stacked widget.