Surprising or less know things from the Ruby on Rails universe
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Rails Tips

Surprising or less know things from the Ruby on Rails universe

How to DRY up my routes?

Perhaps routing concerns can help you. Concern is like a mixin of routes that you can use inside other resources and routes:

concern :taskable do
  resources :tasks, :only => [:index, :create, :destroy]

resources :users, :concerns => :taskable
resources :managers, :concerns => :taskable
resources :admins, :concerns => :taskable

This is the same as:

resources :users do
  resources :tasks, :only => [:index, :create, :destroy]

resources :managers do
  resources :tasks, :only => [:index, :create, :destroy]

resources :admins do
  resources :tasks, :only => [:index, :create, :destroy]

How to send a piece of HTML to a partial?

Do you need to send a piece of HTML to a partial? Perhaps the partial is used on a number of places, but you need to show a different message from each place? You can use Rails' capture helper:

<% personalized_message = capture do %>
  Hi <%= %>! Welcome to the greatest collection of programming books
  in the world!
<% end %>

<%= render "greeting", :message => personalized_message %>

Read more about capture on the official Rails API documentation.

How to Maximize Firefox in a Selenium Test?

Sometimes an end-to-end browser test will fail on a small screen, but pass when it's executed on a large screen. One way to fix this is to maximize the Firefox window that's executing the test. You can do that with this one-liner:


If you want to maximize the Firefox window in all scenarios that execute in Firefox, you should check if the current test is executing in a real browser first. If you're using Cucumber, you can add this to your support/env.rb file:

Before do
  Capybara.current_driver == Capybara.javascript_driver

How to accept a JavaScript dialog in Selenium tests?

Capybara has a neat method called accept_dialog that will do just what you need. Developers used to lean on different JavaScript hacks to accept a JavaScript dialog, but the built in accept_dialog method is the recommended way.

accept_dialog("Are you sure?")

How to skip assets, helpers and specs when generating a controller?

I rarely need assets, helpers and specs for a new controller. And I don't like leaving empty files all over the place. To skip generating those, you can use the following options when you generate a new controller:

rails g controller Posts --no-assets --no-helper --no-controller-specs

You can also use skip instead of no:

rails g controller Posts --skip-assets --skip-helper --skip-controller-specs

If other developers from your team tend to skip those and you want to save some typing, add the following to your config/application.rb:

config.generators do |g|
  g.test_framework nil # skip test framework
  g.assets false
  g.helper false

For more options see Generators page on Rails Guides.

How to wait for a JavaScript library to load in Selenium tests?

Sometimes you need to wait for a JavaScript library to be fully loaded before executing any steps in Selenium tests. To do this, create a helper and make it available in your test library of choice (RSpec, Cucumber...):

module WaitForJqueryUjs
  def wait_for_jquery_ujs
    Timeout.timeout(Capybara.default_wait_time) do
      loop until jquery_ujs_loaded?

  def jquery_ujs_loaded?
    page.evaluate_script("jQuery.rails !== undefined")

Then, in a test, you can use wait_for_jquery_ujs before any steps that require the library:

fill_in "Name", :with => "John Doe"
click_button "Save"

You can use this pattern to inspect other things in JavaScript. However, you should consider leaning on a visible element on a page, instead of executing JavaScript code. For example, you application can show a loading indicator until everything is fully loaded. In tests, you can wait until the loading indicator goes away before executing any steps.

How to add ":type => :model" to all RSpec model specs?

If you're upgrading a gem that's using :type => :model metadata internally, like shoulda-matchers, this can be useful. Just execute this command in your shell:

find spec/models -iname "*.rb" -print | xargs sed -ri "s/describe ([A-Z].*) do/describe \1, :type => :model do/g"