Rails: Overriding view templates under certain conditions only

Rails offers a way to prepend (or append) view paths for the current request. This way, you can make the application use different view templates for just that request.

Example

A use case of this is a different set of view templates that should be used under certain circumstances:

Copyclass UsersController < ApplicationController

  before_action :prepare_views
  
  def index
    # ...
  end    
  
  private
  
  def prepare_views
    if <condition>
      prepend_view_path Rails.root.join('app', 'views', 'special')
    end
  end
  
end

If <condition> is true, Rails will first look into app/views/special to find a view template. E.g. in this example, it would look for app/views/special/users/index.erb before trying the default app/views/users/index.erb.

If the desired template does not exist there, it will fall back to its standard view paths. This way you can customize select templates without needing to redefine all.

Warning

prepend_view_path has a memory leak in many versions of Rails. See the linked article for a fix.