Django dynamic forms - on-the-fly field population?

Question

I've been scanning through Django documentation, and Google search results, all afternoon and I'm still somewhat stuck in my attempt to create a dynamic form. I'm hoping I just need someone to nudge me in the right direction :-) I'm just starting to learn Django, so I'm still very much a beginner; however, I'm already an intermediate python user.

What I'm trying to do is create a dynamic form, where the user makes a selection from a drop-down menu, and based on that selection another part of the form will automatically update to display results relevant to the currently selected item, but from another database table.

I'll try and use a simplified version of the models from the Django tutorial to better illustrate what I'm trying to do:

# models.py
from django.db import models

class Poll(models.Model):
    question = models.CharField(max_length=200)

class Choice(models.Model):
    poll = models.ForeignKey(Poll)
    choice = models.CharField(max_length=200)

So lets say I want to have something like a drop-down selection field, populated with the question from each Poll in the database. I also want to have a text-field, which displays the corresponding choices for the currently selected Poll, which will update on-the-fly whenever the user selects a different Pool. I've been able to figure this out by placing a button, and posting information back to the form; However, I'm trying to do this automatically as the user makes a selection. My view sort of looks something like this at the moment:

#view.py
from django import forms
from django.shortcuts import render_to_response

from myapp.models import Poll,Choice

class MyModelChoiceField(forms.ModelChoiceField):
    def label_from_instance(self, obj):
        return "%s" % obj.question

class PollSelectionForm(forms.Form):
    polls = MyModelChoiceField( queryset=Poll.objects.all() )

class ChoiceResults(forms.Form):
    def __init__(self, newid, *args, **kwargs):
        super(ChoiceResults, self).__init__(*args, **kwargs)

        self.fields['choice'] = forms.TextField( initial="" )

def main(request):
    return render_to_response("myapp/index.html", {
        "object": PollSelectionForm(), 
        "object2": ChoiceResults(),
    })

My template is very simple, just something like

{{ object }}
{{ object2 }}

I'm sure the way I'm going about creating the forms is probably not the best either, so feel free to criticize that as well :-) As I mentioned, I've read solutions involving reposting the form, but I want this to happen on-the-fly... if I can repost transparently then that would be fine I guess. I've also seen libraries that will let you dynamically create forms, but that just seems like overkill.

Answer 1

Here is one approach - Django/jQuery Cascading Select Boxes?

You can create a new view that just renders json to a string, and then trigger an event when you're done selecting from the first list which loads the data dynamically from that json.