Routing based on indices in an array in rails 3 using mongoMapper

I have two models, Trip and Day, with a one-to-many relationship. For the time being I do not want to make Day an embedded document.

class Day
  include MongoMapper::Document
  ...
  key :trip_id, ObjectId
  belongs_to :trip
end

class Trip
  include MongoMapper::Document
  ...
  key :day_ids, Array
  many :days, :in => :day_ids
end

I would like to be able to create routes that look like this:

/trips/:trip_id/days/:index_of_day

Where :index_of_day would be used to find the nth day in a trip @trip.days[:index_of_day], so a person could easily navigate to the first, second, etc. day of a trip.

Currently my route.rb file looks like this:

resources :trips do
  resources :days
end

Which generates the default routes /trips/:trip_id/days/:day_id.

One partway solution I had was to put in my route.rb file

match 'trips/:trip_id/day/:id' => 'days#show'

And then in my Day开发者_如何学Pythons Controller

def show
  @day = Trip.find(params[:trip_id]).days(params[:id].to_i)
  ...
end

This sort of worked except all of the helpers like trip_day_path automatically redirect using the day id, not the day index.

If you want your helpers to use the index instead of the day id, you can define to_param in your Day model. Rails calls to_param on your object to find out what to put in the URL.

class Day
  # ...

  # many :in is for many-to-many, but you are using it for one-to-many
  # either way, many :in doesn't have an inverse yet
  def trip
    Trip.first('day_ids' => self.id)
  end

  def to_param
    trip.days.find_index(self)
  end
end

You'll notice that's kind of hackish, which is a code smell.