Dynamic fields in forms

Rails
1

Hi all.

I am developing a rails app, more or less a car database.

The interresting part of the model is this :
Country (has_many) <-> (belongs_to) Car maker (has_many) <->
(belongs_to) model etc. But some categories are off this dependency
relationship, as for instance, Vintage, motors,…

The problem I am facing is making a new.rhtml file. More precisely, this
kind of apps needs whether:

  1. not to show the model until the country and the car maker have been
    selected
  2. (optional) the upper categories are automatically set when a sub
    category is selected. For example : US - Ford appear when Mustang is
    selected in the form.

I’ve got a couple of books on rails I work on, but non goes on this
subject.

I imagine that Ajax will be part of the answer and yet nothing like this
has resulted so far on gg.

Any help most welcome!

Alex Mic

2

Making myself clearer on the 1) up there :
The fields can or cannot be shown until the upper categories are filled,
but if shown they are blank or unselectable.