python - 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.