Django admin inline forms - limit foreign key queryset to a set of values


I have some interrelated models that need to co-exist on a single admin page. Here's the idea:

Theater productions have cast members, and cast members have specified roles. A theater production is related to a given written text (play, adaptation, etc.), and the written text holds a list of all the roles for that text. When adding a Production, each cast member needs to be associated with one of those roles.

Here's how the data model is working:

Models: Production, Person, CastMember, Role, WrittenText

Relationships: Production and Person have an M2M relationship through CastMember, which adds a "role" field - a ForeignKey to a Role object. Role itself has a ForeignKey to a WrittenText object.

So, the problem is this: in the admin page for Productions, I have a TabularInline to add CastMembers. The CastMember entries in the table should have their 'role' field limited to only the roles specified in the WrittenText that the Production references.

I made a half-way solution to the problem by overriding the model form:

class CastMemberForm(ModelForm): class Meta: model = CastMember def __init__(self, *args, **kwargs): super(CastMemberForm, self).__init__(*args, **kwargs) if 'instance' in kwargs: self.fields['role'].queryset = Role.objects.filter(source_text=self.instance.production.source_text)

But, this only works if you choose a Person from the drop-down, save, and then choose the role - otherwise you just get a list of all roles. Taking out "if 'instance' in kwargs" gives me a DoesNotExistError.

Is this just way too complex to do without something like client-side JS, or is there a simpler solution that I'm missing?


<a href="http://djangosnippets.org/snippets/1028/" rel="nofollow">Here</a> is an example of chained select boxes via javascript/ajax. It should basically be the same principle, but you should need to tweak the js to not update one select box, but all of them in the inline admin... Maybe this gives you a small inspiration!


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