Best way to add a second parameter to route - ruby-on-rails-3

Question

I want my route to be something like cars(/:country/):car_id, what is the best way to do that? Only "cars" will list all the cars and "cars /: country" will list all the cars that are made in that country.
Now I have my route like this resources: cars,: path => "cars (/:country)" and I check in cars#index action if params[:country] is nil to determine what will be retrieved from the database .
My solution feels wrong and ugly and I guess the best solution and cleanest would be to make a country model, but do not really know how to organize it all up, tips?
country must have a slug and so do car_id too (using friendly_id for car_id). It feels like I should have a car table with name and slug thats all i have figured out.
Thanks!

Answer 1

First I'd say that your current solution is NOT ugly, nor wrong, at worst it's pedestrian. But without seeing all the involved models and associations, I can only give a general answer.
First, A country model, probably a good idea, but how do you relate it to the cars model?
You could do this:
class Country << ActiveRecord::Base
has_may :cars
end
class Car << ActiveRecord::Base
belongs_to :country
end
That would support semantics where by you could select a country, and get all cars belonging to a certain country, i.e.
#cars = Country.find('USA').cars
OR, you could do something like:
class Car << ActiveRecord::Base
has_one :country
end
class Country << ActiveRecord::Base
end
That would enable a different semantic:
#country = Car.find('Jeep').country
The point is to think of the query semantics you'd like to have in your app, and then define your associations to support the semantics that make sense for your app. I've posted very simple associations, you may end up with multiple and more complex associations, just depends on how you need to query the database and the associated models.
UPDATE
You posted:
I want my route to be something like cars(/:country/):car_id,
That doesn't make sense, if you know the specific car_id, you don't need any filtering or extra searching.
Sound like you want these URLs:
/cars # all cars
/cars/:country # all cars in country
/car/:id # a specific car
The first and third routes are probably there assuming you've defined the full set of RESTful routes for cars, i.e.
config/routes.rb
resources :cars
You just need to add to routes.rb:
GET '/cars/:country' => 'cars#index'
Then in app/controllers/cars_controller.rb:
def index
if params[:country]
#cars = Car.where("country_id = ?", params[:country])
else
#cars = Car.all
end
end
This assumes you have a relationship set up whereby each car record has a country_id attribute. That can come about in several ways, for example:
class Car < ActiveRecord::Base
belongs_to :country
end
That says my car table has a country_id attribute, and I can do something like:
#car = Car.find(1001)
"The car is in #{#car.country.name}"