How Does One Implement Dynamic 404, 500, etc Error Pages in Rails?

Question

How does one implement dynamic, custom error pages in Rails?

For example a custom 404 error page using your application.html.erb layout and some dynamic fields in the page.

Also, how does one test this from a local machine?

Answer 1

I looked at a few blog posts on Google on how to do this, unfortunately most seem to rely on polluting your ApplicationController.

What I did instead was to create a template with the 404 message then use that template to update the public/404.html file from a rake task:

# Rake file to generate static 404 page

file "public/404.html" => ["app/views/layouts/application.html.erb"] do |t|
    print "Updating 404 page\n"
    `curl --silent http://locahost/content/error404 -o public/404.html`
end 

Now whenever I update my global layout the 404 page gets updated automatically.

Answer 2

just add the following to your ApplicationController:

  rescue_from ActiveRecord::RecordNotFound, :with => :render_record_not_found

  # Catch record not found for Active Record
  def render_record_not_found
    render :template => "shared/catchmissingpage", :layout => false, :status => 404
  end

  # Catches any missing methods and calls the general render_missing_page method
  def method_missing(*args)
    render_missing_page # calls my common 404 rendering method
  end

  # General method to render a 404
  def render_missing_page
    render :template => "shared/catchmissingpage", :layout => false, :status => 404
  end

You can customize the render call (use your templates, use a layout etc.) and catch errors this way. Now it catches missing method and record_not_found for you, but maybe there are cases where you want to display a 500 Error page so you can just go ahead, use this approach and make it fit for you.

For testing from a local machine, it just works like that. if you only want it to work in production mode, add a

 if ENV['RAILS_ENV'] == 'production'

and you're fine.