Namespacing views by subdomain in RailsFebruary 15th, 2016Cristiano Betta2 minute read

Yesterday I wrote about namespacing and scoping a Rails app to separate concerns and today I want to extend this to subdomains.

On the BattleHack site we serve every year from the same app (e.g. 2014 and 2015) while displaying different layouts. To do this we use the same controllers for each year (every one of them inheriting from controllers/app/base_controller.rb).

Extracting the subdomain

In the base controller I first extract the current year:

# /app/controllers/app/base_controller.rb

def selected_year
  @selected_year ||= begin
    if ["2014", "2015"].include?(request.subdomain)
      request.subdomain
    else
      "2015"
    end
  end
end

A few things to note here:

• I whitelist the acceptable subdomains as the alternative would allow anyone to access any view paths, potentially opening the app up to unexpected and insecure behaviour.
• When the subdomain is blank or not in the whitelist I instead return the default year. You could put this in an environment variabe instead of hardcoding it like I did here.

Layouts and views

Next up I changed the base controllers to use the current year to load the correct layout and views.

# /app/controllers/app/base_controller.rb

class App::BaseController < ApplicationController
  layout -> { selected_year }

  before_filter :set_view_path

  def set_view_path
    prepend_view_path("app/views/#{selected_year}")
  end

  ...
end

With this setup your controllers will default to:

• /app/views/layouts/2015.html.erb as a layout
• /app/views/2015/app/ as their view path

Caveats

One big caveat with this setup is that any changes in your models or controllers will require changes in every template for every year. If you remove an attribute on a model, or change the representation of an attribute, this will affect every subdomain.

There are a few solutions to this (besides good tests). One way is to use the presenter pattern (and using a separate presenter based on each subdomain) to keep your changes from breaking anything. Alternatively you can also rely on helpers per subdomain to achieve a similar effect.