RoR Difficulty accessing params in controller - ruby-on-rails-3

Question

I have an edit page with the following code, basically a dropdown and button that calls update.
<% form_tag('switch_car', :method => :put) do%>
<div class="field">
<label>Car Name:</label>
<%= select("params", ":id", #available_cars.collect {|v| [v.name, v.id]})%>
</div>
<div>
<%= submit_tag "Switch Car" %>
</div>
<% end %>
The server reads like the params is being set:
Parameters: {"utf8"=>"Γ£ô", "authenticity_token"=>"8vHXrnICaOKrGns6FfMUcd/dWo5kpNKpA8F5l5ozRkY=", "params"=>{":id"=>"9"}, "commit"=>"Switch Car"}
However, when I put the params into a session I get nothing. It seems to be always nil. Not sure what I am doing wrong? Here is code in the controller.
def update
if params[:id]
session[:car_info_id] = params[:id]
redirect_to entry_url
else
redirect_to switch_car_path
end
end
It always gets redirected to the switch_car_path so I am assuming params[:id] is always nil. When I put if params[:id] == nil it goes to the entry_url.
Thanks in advance.

Answer 1

you want params[:params][":id"]
Alternatively, you could put this in your view:<%= select("car_info", "id", #available_cars.collect {|v| [v.name, v.id]})%>
And then in your controller:if params[:car_info][:id]

Answer 2

While the other answer would work, this is probably what you'd want to be doing (using select_tag(:id) will automatically add an :id key/value to the params hash):
<% form_tag('switch_car', :method => :put) do %>
<div class="field">
<label>Car Name:</label>
<%= select_tag(:id, options_from_collection_for_select(#available_cars, "id", "name")) %>
</div>
<div>
<%= submit_tag "Switch Car" %>
</div>
<% end %>
Then you can easily access params[:id] in the controller.