🎓 Renaming route parameters

When you are looking up models from your controller, using anything other than the model id, the code you write starts to look unusual.

# app/controllers/trains_controller.rb

class TrainsController < ApplicationController
  def show
    @train = Train.find_by(reference: params.fetch(:id))
  end
end

We’re looking up the Train record by its reference using a parameter named id.

To avoid confusion we can tell Rails to name the id parameter to something else that would make more sense to us, for example reference. We achieve this by slightly modifying the routes file.

# config/routes.rb

resources :trains, param: :reference

After adding the param: :reference we can now access the parameter in out controller using params.fetch(:reference) allowing our controller to be more explicit.

# app/controllers/trains_controller.rb

class TrainsController < ApplicationController
  def show
    @train = Train.find_by(reference: params.fetch(:reference))
  end
end

We can now say that we’re looking up the Train record by its reference using a parameter named reference.

The URL pattern has now changed from trains/:id to trains/:reference. This works for nested routes too, Rails adds the appropriate prefix to the parameter trains/:train_reference/timetables.