Rails based simple AJAX calculation fxn seems harder than it should be - ruby

Question

I feel like there is a large step from where Rails tutorials end and where I can actually use it to do what I need. This is manifesting itself in this relatively simple case:
I want a page that takes inputs and calculates a volume. Ideally, this would do it with AJAX because it always irritates me when a simple page makes me reload it.
I've been doing this in IRB with:
radius = 25; length = 0.15;( radius**2) * Math::PI * length *1e-3
# radius in microns, length in meters, answer in microliters
But the confusion comes in just about here. I understand that I must route a page, I understand that my controller is responsible for directing to the correct response, but where should my calculation occur? How do I capture the responses for my form?
I just don't seem to understand how to integrate all these things...
Here's my view (which renders, but from which I can't seem to feed the information in or out:
<h2>Here I'll calculate the dead volume of a piece of tubing for you.</h2>
<%= form_tag url_for(:method => :get), :remote => true, :id => 'calculation_entry' do %>
<div id="internal_diameter">
<label for="diameter">Enter the internal diameter:</label>
<%= text_field_tag :diameter %>
<label for="diameter_unit"></label>
<%= select_tag :diameter_unit, options_for_select({
"Microns" => 'micrometers',
'inches' => 'inches'
}) %>
</div>
<div id="length">
<label for="length">Enter the length of tubing:</label>
<%= text_field_tag :length %>
<label for="length_unit"></label>
<%= select_tag :length_unit, options_for_select({
"meters" => 'meters',
"inches" => 'inches'
}) %>
</div>
<%= submit_tag "Calculate!" %>
<% end %>
<div class="output">
<span>The volume of the tubing parameters entered is:</span>
<%= #object %>
</div>
And here is the controller I've built:
class PagesController < ApplicationController
def index
end
def dead_volume
#object = Object.new
end
def calculate
#object = params.inspect
end
end

Answer 1

Here is an example of how I implemented autocomplete functionality with jQuery UI & Ajax. It may help you to determine how to do this for your own application's needs.
Note: This is was done under Rails 3.0.X. There are probably other/better ways to do this.
View/Layout:
<div id="search">
<%= form_tag('/<my_controller>/search', :method => :get, :id => "#search-text") do %>
<input type="text" name="search" value="" id="search-text" placeholder="Search">
<input type="submit" value="Go" class="button">
<% end %>
</div>
JavaScript (note: uses jQuery UI):
$(document).ready(function() {
$("#search-text").autocomplete({
source: function(request, response) {
$.getJSON("/<my_controller>/autocomplete", {
search: request.term
},
response);
},
minLength: 2,
select: function(event, ui) {
this.value = ui.item.value;
return false;
},
});
});
Route:
match '/<my_controller>/autocomplete' => '<my_controller>#autocomplete', :via => :get
Controller:
respond_to :json, :only => [:autocomplete]
def autocomplete
#model = Model.autocomplete(params[:search])
render(:json => #model)
end
I hope this helps you get on your way.