[Answer]-Interdependent dropdowns Django JQuery Ajax – getting the url right

In your views def all_json_models(request, product_type): the URL controller ^order/(?P<brand>[-\w]+)/all_json_models/$ call the view with the parameter brand not product_type !

For more protection you can modify the ^order/(?P<brand>[-\w]+)/all_json_models/$ to only capture an ID, since you send the product_type id and not the product_type itself, ^order/(?P<brand>[-\d]+)/all_json_models/$. What you can do is send the product_type itself, it helps for the SEO !

You need to be more careful about your code, and the way you treat and capture exceptions !

Also: The MIME media type for JSON text is application/json. The default encoding is UTF-8. (Source: RFC 4627).

In urls.py you are using the tutorial syntax, but using your own in the view.

Try:

(r'^order/(?P<product_type>[-\w]+)/all_json_models/$', 'all_json_models'),