Prelude

Role models are important.
-- Officer Alex J. Murphy / RoboCop

The goal of this guide is to present a set of best practices and style prescriptions for Ruby on Rails 4 development. It's a complementary guide to the already existing community-driven Ruby coding style guide.

Some of the advice here is applicable only to Rails 4.0+.

You can generate a PDF or an HTML copy of this guide using Pandoc.

Translations of the guide are available in the following languages:

• Chinese Simplified
• Chinese Traditional
• German
• Japanese
• Russian
• Turkish
• Korean

The Rails Style Guide

This Rails style guide recommends best practices so that real-world Rails programmers can write code that can be maintained by other real-world Rails programmers. A style guide that reflects real-world usage gets used, and a style guide that holds to an ideal that has been rejected by the people it is supposed to help risks not getting used at all – no matter how good it is.

The guide is separated into several sections of related rules. I've tried to add the rationale behind the rules (if it's omitted I've assumed it's pretty obvious).

I didn't come up with all the rules out of nowhere - they are mostly based on my extensive career as a professional software engineer, feedback and suggestions from members of the Rails community and various highly regarded Rails programming resources.

Table of Contents

• Configuration
• Routing
• Controllers
  • Rendering
• Models
  • ActiveRecord
  • ActiveRecord Queries
• Migrations
• Views
• Internationalization
• Assets
• Mailers
• Active Support Core Extensions
• Time
• Bundler
• Managing processes

Configuration

• Put custom initialization code in config/initializers. The code in initializers executes on application startup. ^[link]

• Keep initialization code for each gem in a separate file with the same name as the gem, for example carrierwave.rb, active_admin.rb, etc. ^[link]

• Adjust accordingly the settings for development, test and production environment (in the corresponding files under config/environments/) ^[link]

  • Mark additional assets for precompilation (if any):

    # config/environments/production.rb
    # Precompile additional assets (application.js, application.css,
    #and all non-JS/CSS are already added)
    config.assets.precompile += %w( rails_admin/rails_admin.css rails_admin/rails_admin.js )

• Keep configuration that's applicable to all environments in the config/application.rb file. ^[link]

• Create an additional staging environment that closely resembles the production one. ^[link]

• Keep any additional configuration in YAML files under the config/ directory. ^[link]

  Since Rails 4.2 YAML configuration files can be easily loaded with the new config_for method:

  Rails::Application.config_for(:yaml_file)

Routing

• When you need to add more actions to a RESTful resource (do you really need them at all?) use member and collection routes. ^[link]

  # bad
  get 'subscriptions/:id/unsubscribe'
  resources :subscriptions
  
  # good
  resources :subscriptions do
    get 'unsubscribe', on: :member
  end
  
  # bad
  get 'photos/search'
  resources :photos
  
  # good
  resources :photos do
    get 'search', on: :collection
  end

• If you need to define multiple member/collection routes use the alternative block syntax. ^[link]

  resources :subscriptions do
    member do
      get 'unsubscribe'
      # more routes
    end
  end
  
  resources :photos do
    collection do
      get 'search'
      # more routes
    end
  end

• Use nested routes to express better the relationship between ActiveRecord models. ^[link]

  class Post < ActiveRecord::Base
    has_many :comments
  end
  
  class Comments < ActiveRecord::Base
    belongs_to :post
  end
  
  # routes.rb
  resources :posts do
    resources :comments
  end

• If you need to nest routes more than 1 level deep then use the shallow: true option. This will save user from long urls posts/1/comments/5/versions/7/edit and you from long url helpers edit_post_comment_version.

  resources :posts, shallow: true do
    resources :comments do
      resources :versions
    end
  end

• Use namespaced routes to group related actions. ^[link]

  namespace :admin do
    # Directs /admin/products/* to Admin::ProductsController
    # (app/controllers/admin/products_controller.rb)
    resources :products
  end

• Never use the legacy wild controller route. This route will make all actions in every controller accessible via GET requests. ^[link]

  # very bad
  match ':controller(/:action(/:id(.:format)))'

• Don't use match to define any routes unless there is need to map multiple request types among [:get, :post, :patch, :put, :delete] to a single action using :via option. ^[link]

Controllers

• Keep the controllers skinny - they should only retrieve data for the view layer and shouldn't contain any business logic (all the business logic should naturally reside in the model). ^[link]

• Each controller action should (ideally) invoke only one method other than an initial find or new. ^[link]

• Share no more than two instance variables between a controller and a view. ^[link]

Rendering

• Prefer using a template over inline rendering. ^[link]

# very bad
class ProductsController < ApplicationController
  def index
    render inline: "<% products.each do |p| %><p><%= p.name %></p><% end %>", type: :erb
  end
end

# good
## app/views/products/index.html.erb
<%= render partial: 'product', collection: products %>

## app/views/products/_product.html.erb
<p><%= product.name %></p>
<p><%= product.price %></p>

## app/controllers/foo_controller.rb
class ProductsController < ApplicationController
  def index
    render :index
  end
end

• Prefer render plain: over render text:. ^[link]

# bad - sets MIME type to `text/html`
...
render text: 'Ruby!'
...

# bad - requires explicit MIME type declaration
...
render text: 'Ruby!', content_type: 'text/plain'
...

# good - short and precise
...
render plain: 'Ruby!'
...

• Prefer corresponding symbols to numeric HTTP status codes. They are meaningful and do not look like "magic" numbers for less known HTTP status codes. ^[link]

# bad
...
render status: 500
...

# good
...
render status: :forbidden
...

Models

• Introduce non-ActiveRecord model classes freely. ^[link]

• Name the models with meaningful (but short) names without abbreviations. ^[link]

• If you need model objects that support ActiveRecord behavior (like validation) without the ActiveRecord database functionality use the ActiveAttr gem. ^[link]

  class Message
    include ActiveAttr::Model
  
    attribute :name
    attribute :email
    attribute :content
    attribute :priority
  
    attr_accessible :name, :email, :content
  
    validates :name, presence: true
    validates :email, format: { with: /\A[-a-z0-9_+\.]+\@([-a-z0-9]+\.)+[a-z0-9]{2,4}\z/i }
    validates :content, length: { maximum: 500 }
  end

  For a more complete example refer to the RailsCast on the subject.

• Unless they have some meaning in the business domain, don't put methods in your model that just format your data (like code generating HTML). These methods are most likely going to be called from the view layer only, so their place is in helpers. Keep your models for business logic and data-persistence only. ^[link]

ActiveRecord

• Avoid altering ActiveRecord defaults (table names, primary key, etc) unless you have a very good reason (like a database that's not under your control). ^[link]

  # bad - don't do this if you can modify the schema
  class Transaction < ActiveRecord::Base
    self.table_name = 'order'
    ...
  end

• Group macro-style methods (has_many, validates, etc) in the beginning of the class definition. ^[link]

  class User < ActiveRecord::Base
    # keep the default scope first (if any)
    default_scope { where(active: true) }
  
    # constants come up next
    COLORS = %w(red green blue)
  
    # afterwards we put attr related macros
    attr_accessor :formatted_date_of_birth
  
    attr_accessible :login, :first_name, :last_name, :email, :password
  
    # Rails4+ enums after attr macros, prefer the hash syntax
    enum gender: { female: 0, male: 1 }
  
    # followed by association macros
    belongs_to :country
  
    has_many :authentications, dependent: :destroy
  
    # and validation macros
    validates :email, presence: true
    validates :username, presence: true
    validates :username, uniqueness: { case_sensitive: false }
    validates :username, format: { with: /\A[A-Za-z][A-Za-z0-9._-]{2,19}\z/ }
    validates :password, format: { with: /\A\S{8,128}\z/, allow_nil: true }
  
    # next we have callbacks
    before_save :cook
    before_save :update_username_lower
  
    # other macros (like devise's) should be placed after the callbacks
  
    ...
  end

• Prefer has_many :through to has_and_belongs_to_many. Using has_many :through allows additional attributes and validations on the join model. ^[link]

  # not so good - using has_and_belongs_to_many
  class User < ActiveRecord::Base
    has_and_belongs_to_many :groups
  end
  
  class Group < ActiveRecord::Base
    has_and_belongs_to_many :users
  end
  
  # preferred way - using has_many :through
  class User < ActiveRecord::Base
    has_many :memberships
    has_many :groups, through: :memberships
  end
  
  class Membership < ActiveRecord::Base
    belongs_to :user
    belongs_to :group
  end
  
  class Group < ActiveRecord::Base
    has_many :memberships
    has_many :users, through: :memberships
  end

• Prefer self[:attribute] over read_attribute(:attribute). ^[link]

  # bad
  def amount
    read_attribute(:amount) * 100
  end
  
  # good
  def amount
    self[:amount] * 100
  end

• Prefer self[:attribute] = value over write_attribute(:attribute, value). ^[link]

  # bad
  def amount
    write_attribute(:amount, 100)
  end
  
  # good
  def amount
    self[:amount] = 100
  end

• Always use the new "sexy" validations. ^[link]

  # bad
  validates_presence_of :email
  validates_length_of :email, maximum: 100
  
  # good
  validates :email, presence: true, length: { maximum: 100 }

• When a custom validation is used more than once or the validation is some regular expression mapping, create a custom validator file. ^[link]

  # bad
  class Person
    validates :email, format: { with: /\A([^@\s]+)@((?:[-a-z0-9]+\.)+[a-z]{2,})\z/i }
  end
  
  # good
  class EmailValidator < ActiveModel::EachValidator
    def validate_each(record, attribute, value)
      record.errors[attribute] << (options[:message] || 'is not a valid email') unless value =~ /\A([^@\s]+)@((?:[-a-z0-9]+\.)+[a-z]{2,})\z/i
    end
  end
  
  class Person
    validates :email, email: true
  end

• Keep custom validators under app/validators. ^[link]

• Consider extracting custom validators to a shared gem if you're maintaining several related apps or the validators are generic enough. ^[link]

• Use named scopes freely. ^[link]

  class User < ActiveRecord::Base
    scope :active, -> { where(active: true) }
    scope :inactive, -> { where(active: false) }
  
    scope :with_orders, -> { joins(:orders).select('distinct(users.id)') }
  end

• When a named scope defined with a lambda and parameters becomes too complicated, it is preferable to make a class method instead which serves the same purpose of the named scope and returns an ActiveRecord::Relation object. Arguably you can define even simpler scopes like this. ^[link]

  class User < ActiveRecord::Base
    def self.with_orders
      joins(:orders).select('distinct(users.id)')
    end
  end

• Beware of the behavior of the update_attribute method. It doesn't run the model validations (unlike update_attributes) and could easily corrupt the model state. ^[link]

• Use user-friendly URLs. Show some descriptive attribute of the model in the URL rather than its id. There is more than one way to achieve this: ^[link]

  • Override the to_param method of the model. This method is used by Rails for constructing a URL to the object. The default implementation returns the id of the record as a String. It could be overridden to include another human-readable attribute.

    class Person
      def to_param
        "#{id} #{name}".parameterize
      end
    end

  In order to convert this to a URL-friendly value, parameterize should be called on the string. The id of the object needs to be at the beginning so that it can be found by the find method of ActiveRecord.

  • Use the friendly_id gem. It allows creation of human-readable URLs by using some descriptive attribute of the model instead of its id.

    class Person
      extend FriendlyId
      friendly_id :name, use: :slugged
    end

  Check the gem documentation for more information about its usage.

• Use find_each to iterate over a collection of AR objects. Looping through a collection of records from the database (using the all method, for example) is very inefficient since it will try to instantiate all the objects at once. In that case, batch processing methods allow you to work with the records in batches, thereby greatly reducing memory consumption. ^[link]

  # bad
  Person.all.each do |person|
    person.do_awesome_stuff
  end
  
  Person.where('age > 21').each do |person|
    person.party_all_night!
  end
  
  # good
  Person.find_each do |person|
    person.do_awesome_stuff
  end
  
  Person.where('age > 21').find_each do |person|
    person.party_all_night!
  end

• Since Rails creates callbacks for dependent associations, always call before_destroy callbacks that perform validation with prepend: true. ^[link]

  # bad (roles will be deleted automatically even if super_admin? is true)
  has_many :roles, dependent: :destroy
  
  before_destroy :ensure_deletable
  
  def ensure_deletable
    fail "Cannot delete super admin." if super_admin?
  end
  
  # good
  has_many :roles, dependent: :destroy
  
  before_destroy :ensure_deletable, prepend: true
  
  def ensure_deletable
    fail "Cannot delete super admin." if super_admin?
  end

• Define the dependent option to the has_many and has_one associations. ^[link]

  # bad
  class Post < ActiveRecord::Base
    has_many :comments
  end
  
  # good
  class Post < ActiveRecord::Base
    has_many :comments, dependent: :destroy
  end

ActiveRecord Queries

• Avoid string interpolation in queries, as it will make your code susceptible to SQL injection attacks. ^[link]

  # bad - param will be interpolated unescaped
  Client.where("orders_count = #{params[:orders]}")
  
  # good - param will be properly escaped
  Client.where('orders_count = ?', params[:orders])

• Consider using named placeholders instead of positional placeholders when you have more than 1 placeholder in your query. ^[link]

  # okish
  Client.where(
    'created_at >= ? AND created_at <= ?',
    params[:start_date], params[:end_date]
  )
  
  # good
  Client.where(
    'created_at >= :start_date AND created_at <= :end_date',
    start_date: params[:start_date], end_date: params[:end_date]
  )

• Favor the use of find over where when you need to retrieve a single record by id. ^[link]

  # bad
  User.where(id: id).take
  
  # good
  User.find(id)

• Favor the use of find_by over where and find_by_attribute when you need to retrieve a single record by some attributes. ^[link]

  # bad
  User.where(first_name: 'Bruce', last_name: 'Wayne').first
  
  # bad
  User.find_by_first_name_and_last_name('Bruce', 'Wayne')
  
  # good
  User.find_by(first_name: 'Bruce', last_name: 'Wayne')

• Favor the use of where.not over SQL. ^[link]

  # bad
  User.where("id != ?", id)
  
  # good
  User.where.not(id: id)

• When specifying an explicit query in a method such as find_by_sql, use heredocs with squish. This allows you to legibly format the SQL with line breaks and indentations, while supporting syntax highlighting in many tools (including GitHub, Atom, and RubyMine). ^[link]

  User.find_by_sql(<<SQL.squish)
    SELECT
      users.id, accounts.plan
    FROM
      users
    INNER JOIN
      accounts
    ON
      accounts.user_id = users.id
    # further complexities...
  SQL

  String#squish removes the indentation and newline characters so that your server log shows a fluid string of SQL rather than something like this:

  SELECT\n    users.id, accounts.plan\n  FROM\n    users\n  INNER JOIN\n    acounts\n  ON\n    accounts.user_id = users.id
  

Migrations

• Keep the schema.rb (or structure.sql) under version control. ^[link]

• Use rake db:schema:load instead of rake db:migrate to initialize an empty database. ^[link]

• Enforce default values in the migrations themselves instead of in the application layer. ^[link]

  # bad - application enforced default value
  def amount
    self[:amount] or 0
  end

  While enforcing table defaults only in Rails is suggested by many Rails developers, it's an extremely brittle approach that leaves your data vulnerable to many application bugs. And you'll have to consider the fact that most non-trivial apps share a database with other applications, so imposing data integrity from the Rails app is impossible.

• Enforce foreign-key constraints. As of Rails 4.2, ActiveRecord supports foreign key constraints natively. ^[link]

• When writing constructive migrations (adding tables or columns), use the change method instead of up and down methods. ^[link]

  # the old way
  class AddNameToPeople < ActiveRecord::Migration
    def up
      add_column :people, :name, :string
    end
  
    def down
      remove_column :people, :name
    end
  end
  
  # the new preferred way
  class AddNameToPeople < ActiveRecord::Migration
    def change
      add_column :people, :name, :string
    end
  end

• Don't use model classes in migrations. The model classes are constantly evolving and at some point in the future migrations that used to work might stop, because of changes in the models used. ^[link]

Views

• Never call the model layer directly from a view. ^[link]

• Never make complex formatting in the views, export the formatting to a method in the view helper or the model. ^[link]

• Mitigate code duplication by using partial templates and layouts. ^[link]

Internationalization

• No strings or other locale specific settings should be used in the views, models and controllers. These texts should be moved to the locale files in the config/locales directory. ^[link]

• When the labels of an ActiveRecord model need to be translated, use the activerecord scope: ^[link]

  en:
    activerecord:
      models:
        user: Member
      attributes:
        user:
          name: 'Full name'
  

  Then User.model_name.human will return "Member" and User.human_attribute_name("name") will return "Full name". These translations of the attributes will be used as labels in the views.

• Separate the texts used in the views from translations of ActiveRecord attributes. Place the locale files for the models in a folder locales/models and the texts used in the views in folder locales/views. ^[link]

  • When organization of the locale files is done with additional directories, these directories must be described in the application.rb file in order to be loaded.

    # config/application.rb
    config.i18n.load_path += Dir[Rails.root.join('config', 'locales', '**', '*.{rb,yml}')]

• Place the shared localization options, such as date or currency formats, in files under the root of the locales directory. ^[link]

• Use the short form of the I18n methods: I18n.t instead of I18n.translate and I18n.l instead of I18n.localize. ^[link]

• Use "lazy" lookup for the texts used in views. Let's say we have the following structure: ^[link]

  en:
    users:
      show:
        title: 'User details page'
  

  The value for users.show.title can be looked up in the template app/views/users/show.html.haml like this:

  = t '.title'

• Use the dot-separated keys in the controllers and models instead of specifying the :scope option. The dot-separated call is easier to read and trace the hierarchy. ^[link]

  # bad
  I18n.t :record_invalid, scope: [:activerecord, :errors, :messages]
  
  # good
  I18n.t 'activerecord.errors.messages.record_invalid'

• More detailed information about the Rails I18n can be found in the Rails Guides ^[link]

Assets

Use the assets pipeline to leverage organization within your application.

• Reserve app/assets for custom stylesheets, javascripts, or images. ^[link]

• Use lib/assets for your own libraries that don’t really fit into the scope of the application. ^[link]

• Third party code such as jQuery or bootstrap should be placed in vendor/assets. ^[link]

• When possible, use gemified versions of assets (e.g. jquery-rails, jquery-ui-rails, bootstrap-sass, zurb-foundation). ^[link]

Mailers

• Name the mailers SomethingMailer. Without the Mailer suffix it isn't immediately apparent what's a mailer and which views are related to the mailer. ^[link]

• Provide both HTML and plain-text view templates. ^[link]

• Enable errors raised on failed mail delivery in your development environment. The errors are disabled by default. ^[link]

  # config/environments/development.rb
  
  config.action_mailer.raise_delivery_errors = true

• Use a local SMTP server like Mailcatcher in the development environment. ^[link]

  # config/environments/development.rb
  
  config.action_mailer.smtp_settings = {
    address: 'localhost',
    port: 1025,
    # more settings
  }

• Provide default settings for the host name. ^[link]

  # config/environments/development.rb
  config.action_mailer.default_url_options = { host: "#{local_ip}:3000" }
  
  # config/environments/production.rb
  config.action_mailer.default_url_options = { host: 'your_site.com' }
  
  # in your mailer class
  default_url_options[:host] = 'your_site.com'

• If you need to use a link to your site in an email, always use the _url, not _path methods. The _url methods include the host name and the _path methods don't. ^[link]

  # bad
  You can always find more info about this course
  <%= link_to 'here', course_path(@course) %>
  
  # good
  You can always find more info about this course
  <%= link_to 'here', course_url(@course) %>

• Format the from and to addresses properly. Use the following format: ^[link]

  # in your mailer class
  default from: 'Your Name <info@your_site.com>'

• Make sure that the e-mail delivery method for your test environment is set to test: ^[link]

  # config/environments/test.rb
  
  config.action_mailer.delivery_method = :test

• The delivery method for development and production should be smtp: ^[link]

  # config/environments/development.rb, config/environments/production.rb
  
  config.action_mailer.delivery_method = :smtp

• When sending html emails all styles should be inline, as some mail clients have problems with external styles. This however makes them harder to maintain and leads to code duplication. There are two similar gems that transform the styles and put them in the corresponding html tags: premailer-rails and roadie. ^[link]

• Sending emails while generating page response should be avoided. It causes delays in loading of the page and request can timeout if multiple email are sent. To overcome this emails can be sent in background process with the help of sidekiq gem. ^[link]

Active Support Core Extensions

• Prefer Ruby 2.3's safe navigation operator &. over ActiveSupport#try!. ^[link]

# bad
obj.try! :fly

# good
obj&.fly

• Prefer Ruby's Standard Library methods over ActiveSupport aliases. ^[link]

# bad
'the day'.starts_with? 'th'
'the day'.ends_with? 'ay'

# good
'the day'.start_with? 'th'
'the day'.end_with? 'ay'

• Prefer Ruby's Standard Library over uncommon ActiveSupport extensions. ^[link]

# bad
(1..50).to_a.forty_two
1.in? [1, 2]
'day'.in? 'the day'

# good
(1..50).to_a[41]
[1, 2].include? 1
'the day'.include? 'day'

• Prefer Ruby's comparison operators over ActiveSupport's Array#inquiry, Numeric#inquiry and String#inquiry. ^[link]

# bad - String#inquiry
ruby = 'two'.inquiry
ruby.two?

# good
ruby = 'two'
ruby == 'two'

# bad - Array#inquiry
pets = %w(cat dog).inquiry
pets.gopher?

# good
pets = %w(cat dog)
pets.include? 'cat'

# bad - Numeric#inquiry
0.positive?
0.negative?

# good
0 > 0
0 < 0

Time

• Config your timezone accordingly in application.rb. ^[link]

  config.time_zone = 'Eastern European Time'
  # optional - note it can be only :utc or :local (default is :utc)
  config.active_record.default_timezone = :local

• Don't use Time.parse. ^[link]

  # bad
  Time.parse('2015-03-02 19:05:37') # => Will assume time string given is in the system's time zone.
  
  # good
  Time.zone.parse('2015-03-02 19:05:37') # => Mon, 02 Mar 2015 19:05:37 EET +02:00

• Don't use Time.now. ^[link]

  # bad
  Time.now # => Returns system time and ignores your configured time zone.
  
  # good
  Time.zone.now # => Fri, 12 Mar 2014 22:04:47 EET +02:00
  Time.current # Same thing but shorter.

Bundler

• Put gems used only for development or testing in the appropriate group in the Gemfile. ^[link]

• Use only established gems in your projects. If you're contemplating on including some little-known gem you should do a careful review of its source code first. ^[link]

• OS-specific gems will by default result in a constantly changing Gemfile.lock for projects with multiple developers using different operating systems. Add all OS X specific gems to a darwin group in the Gemfile, and all Linux specific gems to a linux group: ^[link]

  # Gemfile
  group :darwin do
    gem 'rb-fsevent'
    gem 'growl'
  end
  
  group :linux do
    gem 'rb-inotify'
  end

  To require the appropriate gems in the right environment, add the following to config/application.rb:

  platform = RUBY_PLATFORM.match(/(linux|darwin)/)[0].to_sym
  Bundler.require(platform)

• Do not remove the Gemfile.lock from version control. This is not some randomly generated file - it makes sure that all of your team members get the same gem versions when they do a bundle install. ^[link]

Managing processes

• If your projects depends on various external processes use foreman to manage them. ^[link]

Further Reading

There are a few excellent resources on Rails style, that you should consider if you have time to spare:

• The Rails 4 Way
• Ruby on Rails Guides
• The RSpec Book
• The Cucumber Book
• Everyday Rails Testing with RSpec
• Better Specs for RSpec

Contributing

Nothing written in this guide is set in stone. It's my desire to work together with everyone interested in Rails coding style, so that we could ultimately create a resource that will be beneficial to the entire Ruby community.

Feel free to open tickets or send pull requests with improvements. Thanks in advance for your help!

You can also support the project (and RuboCop) with financial contributions via gittip.

How to Contribute?

It's easy, just follow the contribution guidelines.

License

This work is licensed under a Creative Commons Attribution 3.0 Unported License

Spread the Word

A community-driven style guide is of little use to a community that doesn't know about its existence. Tweet about the guide, share it with your friends and colleagues. Every comment, suggestion or opinion we get makes the guide just a little bit better. And we want to have the best possible guide, don't we?

Cheers,
Bozhidar