Custom parameters in URL for show action

I do not see any way to do this with Rails without tweaking either the URL recognition or the URL generation.

With your first attempt, you got the URL recognition working but not the generation. The solution I can see to make the generation working would be to override the car_path helper method.

Another solution could be, like you did in the UPDATE, to override the to_param method of Car. Notice that your problem is not in the to_param method but in the route definition : you need to give :brand,:model_name and :variant parameters when you want to generate the route. To deal with that, you may want to use a Wildcard segment in your route.

Finally you can also use the routing-filter gem which make you able to add logic before and after the url recognition / generation.

For me, it looks like all theses solutions are a bit heavy and not as easy as it should be but I believe this came from your need as you want to add some levels in the URL without strictly following the rails behavior which will give you URL like /brands/audi/models/A3/variants/19930

OK, so here's what I've got. This works in my little test case. Obviously some fixups needed, and I am sure could be more concise and elegant, but my motto is: "make it work, make it pretty, make it fast" :-)

In routes.rb

  controller :cars do
    match 'cars', :to => "cars#index"
    match 'cars/:brand', :to => "cars#list_brand", :as => :brand
    match 'cars/:brand/:model', :to => "cars#list_model_name", :as => :model_name
    match 'cars/:brand/:model/:variant', :to => "cars#list_variant", :as => :variant
  end

In the Car model

  def to_param
    "#{brand}/#{model_name}/#{variant}"
  end

And obviously fragile and non-DRY, in cars_controller.rb

  def index
    @cars = Car.all

    respond_to do |format|
      format.html # index.html.erb
      format.json { render json: @cars }
    end
  end

  def list_brand
    @cars = Car.where("brand = ?", params[:brand])

    respond_to do |format|
      format.html { render :index }
    end
  end

  def list_model_name
    @cars = Car.where("brand = ? and model_name = ?", params[:brand], params[:model])

    respond_to do |format|
      format.html { render :index }
    end
  end

  def list_variant
    @cars = Car.where("brand = ? and model_name = ? and variant = ?", params[:brand], params[:model], params[:variant])

    respond_to do |format|
      format.html { render :index }
    end
  end

You just need to create two routes, one for recognition, one for generation.

Updated: use the routes in question.

# config/routes.rb
# this one is used for path generation
resources :cars, :only => [:index, :show] do
  member do
    get 'favourize'
    get 'unfavourize'
  end
end
# this one is used for path recognition
scope '/cars/:brand/:model_name/:variant' do
  match ':id(/:action)' => 'cars#show', :via => :get
end

And customize to_param

# app/models/car.rb
require 'cgi'

class Car < ActiveRecord::Base
  def to_param
    parts = [brand,
             model_name,
             variant.downcase.gsub(/[^[:alnum:]]/,'-').gsub(/-{2,}/,'-'),
             id]

    parts.collect {|p| p.present? ? CGI.escape(p.to_s) : '-'}.join('/')
  end
end

Sample of path helpers:

link_to 'Show', car_path(@car)
link_to 'Edit', edit_car_path(@car)
link_to 'Favourize', favourize_car_path(@car)
link_to 'Unfavourize', unfavourize_car_path(@car)
link_to 'Cars', cars_path
form_for(@car) # if resources :cars is not
               # restricted to :index and :show

You want bounded parameters to be passed to url of which some parameters are optional and some of them strictly needs to be present.

Rails guides shows you can have strict as well as optional parameters and also you can give name to particular route in-order to simplify its usage.

Guide on rails routing bound parameters

Example usage -

In below route,

• brand is optional parameter as its surrounded by circular bracket

• Also please note there can be optional parameters inside route but they needs to added at last /cars(/:brand)(/:make)(/:model)

  match '/cars/(:brand)', :to => 'cars#index', :as => cars

here cars_url will map to index action of cars controller.. again cars_url("Totoya") will route index action of cars controller along-with params[:brand] as Toyota

Show url route can be as below where id is mandatory and others can be optional

match '/cars/:id(/:brand(/:model_name/)(/:variant)', :to => "cars#show", :as => car

In above case, id is mandatory field. Other parameters are optional. so you can access it like car_url(car.id) or car_url(12, 'toyota') or car_url(12, 'toyota', 'fortuner') or car_url(12, 'toyota', 'fortuner', 'something else)