A way to filter a route based on query params. You can also make the module a class and then initialize it to pass in whatever you want.

routes.rb

module QueryParamConstraint
  extend self

  def matches?(request)
    request.query_parameters["view"] == request.path_parameters[:action]
  end
end


MyPortal::Application.routes.draw do
  root to: 'home#index'
  
  get "/foo" => "people#show", :constraints => QueryParamConstraint
  get "/foo" => "people#index", :constraints => QueryParamConstraint

  resources :people, only: [:index, :show] do
    resources :facts, only: :index
  end
end

Requests would look like.

/foo?view=show
/foo?view=index

We could set up a different query_param for nested routes

/foo?view=index&controller=demographics
/foo?view=show&controller=kids&kid_id=3