rubocop/rails-style-guide

= Rails Style Guide :idprefix: :idseparator: - :sectanchors: :sectlinks: :toc: preamble :toclevels: 1 ifndef::backend-pdf[] :toc-title: pass:[

Table of Contents

] endif::[] :source-highlighter: rouge

== Introduction

By https://github.com/bbatsov[Bozhidar Batsov]

[quote]

---

Role models are important.

-- Officer Alex J. Murphy / RoboCop

---

ifdef::env-github[] TIP: You can find a beautiful version of this guide with much improved navigation at https://rails.rubystyle.guide. endif::[]

The goal of this guide is to present a set of best practices and style prescriptions for Ruby on Rails development. It's a complementary guide to the already existing community-driven https://github.com/rubocop/ruby-style-guide[Ruby coding 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.

NOTE: Some of the advice here is applicable only to recent versions of Rails.

You can generate a PDF copy of this guide using https://asciidoctor.org/docs/asciidoctor-pdf/[AsciiDoctor PDF], and an HTML copy https://asciidoctor.org/docs/convert-documents/#converting-a-document-to-html[with] https://asciidoctor.org/#installation[AsciiDoctor] using the following commands:

[source,shell]

Generates README.pdf

asciidoctor-pdf -a allow-uri-read README.adoc

Generates README.html

asciidoctor README.adoc

[TIP]

Install the rouge gem to get nice syntax highlighting in the generated document.

[source,shell]

gem install rouge

====

Translations of the guide are available in the following languages:

• https://github.com/satour/rails-style-guide/blob/master/README-jaJA.md[Japanese]
• https://github.com/arbox/rails-style-guide/blob/master/README-ruRU.md[Russian]

TIP: https://github.com/rubocop/rubocop[RuboCop], a static code analyzer (linter) and formatter, has a https://github.com/rubocop/rubocop-rails[`rubocop-rails`] extension, based on this style guide.

== Configuration

=== Config Initializers [[config-initializers]]

Put custom initialization code in config/initializers. The code in initializers executes on application startup.

=== Gem Initializers [[gem-initializers]]

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.

=== Dev/Test/Prod Configs [[dev-test-prod-configs]]

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

Mark additional assets for precompilation (if any):

[source,ruby]

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 )

=== App Config [[app-config]]

Keep configuration that's applicable to all environments in the config/application.rb file.

=== Load Rails Config Defaults [[config-defaults]]

When upgrading to a newer Rails version, your application's configuration setting will remain on the previous version. To take advantage of the latest recommended Rails practices, the config.load_defaults setting should match your Rails version.

[source,ruby]

good

config.load_defaults 6.1

=== Staging Like Prod [[staging-like-prod]]

Avoid creating additional environment configurations than the defaults of development, test and production. If you need a production-like environment such as staging, use environment variables for configuration options.

=== YAML Config [[yaml-config]]

Keep any additional configuration in YAML files under the config/ directory.

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

[source,ruby]

Rails::Application.config_for(:yaml_file)

== Routing

=== Member Collection Routes [[member-collection-routes]]

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

[source,ruby]

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

=== Many Member Collection Routes [[many-member-collection-routes]]

If you need to define multiple member/collection routes use the alternative block syntax.

[source,ruby]

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

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

=== Nested Routes [[nested-routes]]

Use nested routes to express better the relationship between Active Record models.

[source,ruby]

class Post < ApplicationRecord has_many :comments end

class Comment < ApplicationRecord belongs_to :post end

routes.rb

resources :posts do resources :comments end

=== Shallow Routes [[shallow-routes]]

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.

[source,ruby]

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

=== Namespaced Routes [[namespaced-routes]]

Use namespaced routes to group related actions.

[source,ruby]

namespace :admin do

Directs /admin/products/* to Admin::ProductsController

(app/controllers/admin/products_controller.rb)

resources :products end

=== No Wild Routes [[no-wild-routes]]

Never use the legacy wild controller route. This route will make all actions in every controller accessible via GET requests.

[source,ruby]

very bad

match ':controller(/:action(/:id(.:format)))'

=== No Match Routes [[no-match-routes]]

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.

== Controllers

=== Skinny Controllers [[skinny-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).

=== One Method [[one-method]]

Each controller action should (ideally) invoke only one method other than an initial find or new.

=== Shared Instance Variables [[shared-instance-variables]]

Minimize the number of instance variables passed between a controller and a view.

=== Lexically Scoped Action Filter [[lexically-scoped-action-filter]]

Controller actions specified in the option of Action Filter should be in lexical scope. The ActionFilter specified for an inherited action makes it difficult to understand the scope of its impact on that action.

[source,ruby]

bad

class UsersController < ApplicationController before_action :require_login, only: :export end

good

class UsersController < ApplicationController before_action :require_login, only: :export

def export end end

== Controllers: Rendering [[rendering]]

=== Inline Rendering [[inline-rendering]]

Prefer using a template over inline rendering.

[source,ruby]

very bad

class ProductsController < ApplicationController def index render inline: "<% products.each do |p| %>

<%= p.name %>

<% end %>", type: :erb end end

good

app/views/products/index.html.erb

<%= render partial: 'product', collection: products %>

app/views/products/_product.html.erb

<%= product.name %>

<%= product.price %>

app/controllers/products_controller.rb

class ProductsController < ApplicationController def index render :index end end

=== Plain Text Rendering [[plain-text-rendering]]

Prefer render plain: over render text:.

[source,ruby]

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!' ...

=== HTTP Status Code Symbols [[http-status-code-symbols]]

Prefer https://gist.github.com/mlanett/a31c340b132ddefa9cca[corresponding symbols] to numeric HTTP status codes. They are meaningful and do not look like "magic" numbers for less known HTTP status codes.

[source,ruby]

bad

... render status: 403 ...

good

... render status: :forbidden ...

== Models

=== Model Classes [[model-classes]]

Introduce non-Active Record model classes freely.

=== Meaningful Model Names [[meaningful-model-names]]

Name the models with meaningful (but short) names without abbreviations.

=== Non-ActiveRecord Models [[non-activerecord-models]]

If you need objects that support ActiveRecord-like behavior (like validations) without the database functionality, use ActiveModel::Model.

[source,ruby]

class Message include ActiveModel::Model

attr_accessor :name, :email, :content, :priority

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

Starting with Rails 6.1, you can also extend the attributes API from ActiveRecord using ActiveModel::Attributes.

[source,ruby]

class Message include ActiveModel::Model include ActiveModel::Attributes

attribute :name, :string attribute :email, :string attribute :content, :string attribute :priority, :integer

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

=== Model Business Logic [[model-business-logic]]

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.

== Models: Active Record [[activerecord]]

=== Keep Active Record Defaults [[keep-ar-defaults]]

Avoid altering Active Record defaults (table names, primary key, etc) unless you have a very good reason (like a database that's not under your control).

[source,ruby]

bad - don't do this if you can modify the schema

class Transaction < ApplicationRecord self.table_name = 'order' ... end

=== Always append to ignored_columns [[append-ignored-columns]]

Avoid setting ignored_columns. It may overwrite previous assignments and that is almost always a mistake. Prefer appending to the list instead.

[source,ruby]

class Transaction < ApplicationRecord

bad - it may overwrite previous assignments

self.ignored_columns = %i[legacy]

good - the value is appended to the list

self.ignored_columns += %i[legacy] ... end

=== Enums [[enums]]

Prefer using the hash syntax for enum. Array makes the database values implicit & any insertion/removal/rearrangement of values in the middle will most probably lead to broken code.

[source,ruby]

class Transaction < ApplicationRecord

bad - implicit values - ordering matters

enum :type, %i[credit debit]

good - explicit values - ordering does not matter

enum :type, { credit: 0, debit: 1 } end

=== Macro Style Methods [[macro-style-methods]]

Group macro-style methods (has_many, validates, etc) in the beginning of the class definition.

[source,ruby]

class User < ApplicationRecord

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

Rails 4+ enums after attr macros

enum role: { user: 0, moderator: 1, admin: 2 }

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

=== has_many :through [[has-many-through]]

Prefer has_many :through to has_and_belongs_to_many. Using has_many :through allows additional attributes and validations on the join model.

[source,ruby]

not so good - using has_and_belongs_to_many

class User < ApplicationRecord has_and_belongs_to_many :groups end

class Group < ApplicationRecord has_and_belongs_to_many :users end

preferred way - using has_many :through

class User < ApplicationRecord has_many :memberships has_many :groups, through: :memberships end

class Membership < ApplicationRecord belongs_to :user belongs_to :group end

class Group < ApplicationRecord has_many :memberships has_many :users, through: :memberships end

=== Read Attribute [[read-attribute]]

Prefer self[:attribute] over read_attribute(:attribute).

[source,ruby]

bad

def amount read_attribute(:amount) * 100 end

good

def amount self[:amount] * 100 end

=== Write Attribute [[write-attribute]]

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

[source,ruby]

bad

def amount write_attribute(:amount, 100) end

good

def amount self[:amount] = 100 end

=== New-style Validations [[new-style-validations]]

Always use the http://thelucid.com/2010/01/08/sexy-validation-in-edge-rails-rails-3/["new-style" validations].

[source,ruby]

bad

validates_presence_of :email validates_length_of :email, maximum: 100

good

validates :email, presence: true, length: { maximum: 100 }

=== Custom Validation Methods

When naming custom validation methods, adhere to the simple rules:

• validate :method_name reads like a natural statement
• the method name explains what it checks
• the method is recognizable as a validation method by its name, not a predicate method

[source,ruby]

good

validate :expiration_date_cannot_be_in_the_past validate :discount_cannot_be_greater_than_total_value validate :ensure_same_topic_is_chosen

also good - explicit prefix

validate :validate_birthday_in_past validate :validate_sufficient_quantity validate :must_have_owner_with_no_other_items validate :must_have_shipping_units

bad

validate :birthday_in_past validate :owner_has_no_other_items

=== Single-attribute Validations [[single-attribute-validations]]

To make validations easy to read, don't list multiple attributes per validation.

[source,ruby]

bad

validates :email, :password, presence: true validates :email, length: { maximum: 100 }

good

validates :email, presence: true, length: { maximum: 100 } validates :password, presence: true

=== Custom Validator File [[custom-validator-file]]

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

[source,ruby]

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

=== App Validators [[app-validators]]

Keep custom validators under app/validators.

=== Custom Validators Gem [[custom-validators-gem]]

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

=== Named Scopes [[named-scopes]]

Use named scopes freely.

[source,ruby]

class User < ApplicationRecord scope :active, -> { where(active: true) } scope :inactive, -> { where(active: false) }

scope :with_orders, -> { joins(:orders).select('distinct(users.id)') } end

=== Named Scope Class [[named-scope-class]]

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.

[source,ruby]

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

=== Callbacks Order [[callbacks-order]]

Order callback declarations in the order in which they will be executed. For reference, see https://guides.rubyonrails.org/active_record_callbacks.html#available-callbacks[Available Callbacks].

[source,ruby]

bad

class Person after_commit :after_commit_callback before_validation :before_validation_callback end

good

class Person before_validation :before_validation_callback after_commit :after_commit_callback end

=== Beware Skip Model Validations [[beware-skip-model-validations]]

Beware of the behavior of the https://guides.rubyonrails.org/active_record_validations.html#skipping-validations[following] methods. They do not run the model validations and could easily corrupt the model state.

[source,ruby]

bad

Article.first.decrement!(:view_count) DiscussionBoard.decrement_counter(:post_count, 5) Article.first.increment!(:view_count) DiscussionBoard.increment_counter(:post_count, 5) person.toggle :active product.touch Billing.update_all("category = 'authorized', author = 'David'") user.update_attribute(:website, 'example.com') user.update_columns(last_request_at: Time.current) Post.update_counters 5, comment_count: -1, action_count: 1

good

user.update_attributes(website: 'example.com')

=== User-friendly URLs [[user-friendly-urls]]

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.

==== 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.

[source,ruby]

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 Active Record.

==== friendly_id Gem

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

[source,ruby]

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

Check the https://github.com/norman/friendly_id[gem documentation] for more information about its usage.

=== find_each [[find-each]]

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.

[source,ruby]

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

=== before_destroy [[before_destroy]]

Since https://github.com/rails/rails/issues/3458[Rails creates callbacks for dependent associations], always call before_destroy callbacks that perform validation with prepend: true.

[source,ruby]

bad (roles will be deleted automatically even if super_admin? is true)

has_many :roles, dependent: :destroy

before_destroy :ensure_deletable

def ensure_deletable raise "Cannot delete super admin." if super_admin? end

good

has_many :roles, dependent: :destroy

before_destroy :ensure_deletable, prepend: true

def ensure_deletable raise "Cannot delete super admin." if super_admin? end

=== has_many/has_one Dependent Option [[has_many-has_one-dependent-option]]

Define the dependent option to the has_many and has_one associations.

[source,ruby]

bad

class Post < ApplicationRecord has_many :comments end

good

class Post < ApplicationRecord has_many :comments, dependent: :destroy end

=== save! [[save-bang]]

When persisting AR objects always use the exception raising bang! method or handle the method return value. This applies to create, save, update, destroy, first_or_create and find_or_create_by.

[source,ruby]

bad

user.create(name: 'Bruce')

bad

user.save

good

user.create!(name: 'Bruce')

or

bruce = user.create(name: 'Bruce') if bruce.persisted? ... else ... end

good

user.save!

or

if user.save ... else ... end

== Models: Active Record Queries [[activerecord-queries]]

=== Avoid Interpolation [[avoid-interpolation]]

Avoid string interpolation in queries, as it will make your code susceptible to SQL injection attacks.

[source,ruby]

bad - param will be interpolated unescaped

Client.where("orders_count = #{params[:orders]}")

good - param will be properly escaped

Client.where('orders_count = ?', params[:orders])

=== Named Placeholder [[named-placeholder]]

Consider using named placeholders instead of positional placeholders when you have more than 1 placeholder in your query.

[source,ruby]

okish

Client.where( 'orders_count >= ? AND country_code = ?', params[:min_orders_count], params[:country_code] )

good

Client.where( 'orders_count >= :min_orders_count AND country_code = :country_code', min_orders_count: params[:min_orders_count], country_code: params[:country_code] )

=== find [[find]]

Prefer find over where.take!, find_by!, and find_by_id! when you need to retrieve a single record by primary key id and raise ActiveRecord::RecordNotFound when the record is not found.

[source,ruby]

bad

User.where(id: id).take!

bad

User.find_by_id!(id)

bad

User.find_by!(id: id)

good

User.find(id)

=== find_by [[find_by]]

Prefer find_by over where.take and find_by_attribute when you need to retrieve a single record by one or more attributes and return nil when the record is not found.

[source,ruby]

bad

User.where(email: email).take User.where(first_name: 'Bruce', last_name: 'Wayne').take

bad

User.find_by_email(email) User.find_by_first_name_and_last_name('Bruce', 'Wayne')

good

User.find_by(email: email) User.find_by(first_name: 'Bruce', last_name: 'Wayne')

=== Hash conditions [[where-not]] [[hash-conditions]]

Prefer passing conditions to where and where.not as a hash over using fragments of SQL.

[source,ruby]

bad

User.where("name = ?", name)

good

User.where(name: name)

bad

User.where("id != ?", id)

good

User.where.not(id: id)

=== Finding missing relationship records [[finding-missing-relationship-records]]

If you're using Rails 6.1 or higher, use https://api.rubyonrails.org/classes/ActiveRecord/QueryMethods/WhereChain.html#method-i-missing[where.missing] to find missing relationship records.

[source,ruby]

bad

Post.left_joins(:author).where(authors: { id: nil })

good

Post.where.missing(:author)

=== Order by id [[order-by-id]]

Don't use the id column for ordering. The sequence of ids is not guaranteed to be in any particular order, despite often (incidentally) being chronological. Use a timestamp column to order chronologically. As a bonus the intent is clearer.

[source,ruby]

bad

scope :chronological, -> { order(id: :asc) }

good

scope :chronological, -> { order(created_at: :asc) }

=== Order arguments [[order-arguments]]

Prefer symbol arguments over strings for ordering.

String columns without a table name can cause an "ambiguous column name" error when ordering by a column that exists in multiple tables joined in the same query.

[source,ruby]

bad

User.order('created_at DESC')

good

User.order(created_at: :desc)

=== pluck

Use https://api.rubyonrails.org/classes/ActiveRecord/Calculations.html#method-i-pluck[pluck] to select a single value from multiple records.

[source,ruby]

bad

User.all.map(&:name)

bad

User.all.map { |user| user[:name] }

good

User.pluck(:name)

=== pick

Use https://api.rubyonrails.org/classes/ActiveRecord/Calculations.html#method-i-pick[pick] to select a single value from a single record.

[source,ruby]

bad

User.pluck(:name).first

bad

User.first.name

good

User.pick(:name)

=== ids [[ids]]

Prefer ids over pluck(:id).

[source,ruby]

bad

User.pluck(:id)

good

User.ids

=== Squished Heredocs [[squished-heredocs]]

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).

[source,ruby]

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

https://api.rubyonrails.org/classes/String.html#method-i-squish[`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 accounts\n ON\n accounts.user_id = users.id

=== size over count or length [[size-over-count-or-length]]

When querying Active Record collections, prefer size (selects between count/length behavior based on whether collection is already loaded) or length (always loads the whole collection and counts the array elements) over count (always does a database query for the count).

[source,ruby]

bad

User.count

good

User.all.size

good - if you really need to load all users into memory

User.all.length

=== Where with Ranges [[where-ranges]]

Use ranges instead of defining comparative conditions using a template for scalar values.

[source,ruby]

bad

User.where("created_at >= ?", 30.days.ago).where("created_at <= ?", 7.days.ago) User.where("created_at >= ? AND created_at <= ?", 30.days.ago, 7.days.ago) User.where("created_at >= :start AND created_at <= :end", start: 30.days.ago, end: 7.days.ago)

good

User.where(created_at: 30.days.ago..7.days.ago)

bad

User.where("created_at >= ?", 7.days.ago)

good

User.where(created_at: 7.days.ago..)

note - ranges are inclusive or exclusive of their ending, not beginning

User.where(created_at: 7.days.ago..) # produces >= User.where(created_at: 7.days.ago...) # also produces >= User.where(created_at: ..7.days.ago) # inclusive: produces <= User.where(created_at: ...7.days.ago) # exclusive: produces <

okish - there is no range syntax that would denote exclusion at the beginning of the range

Customer.where("purchases_count > :min AND purchases_count <= :max", min: 0, max: 5)

NOTE: Rails 6.0 or later is required for endless range Ruby 2.6 syntax, and Rails 6.0.3 for beginless range Ruby 2.7 syntax.

=== where.not with multiple attributes

Avoid passing multiple attributes to where.not. Rails logic in this case has changed in Rails 6.1 and will now yield results matching either of those conditions, e.g. where.not(status: 'active', plan: 'basic') would return records with active status when the plan is business.

[source, ruby]

bad

User.where.not(status: 'active', plan: 'basic')

good

User.where.not('status = ? AND plan = ?', 'active', 'basic')

=== Redundant all [[redundant-all]]

Using all as a receiver is redundant. The result won't change without all, so it should be removed.

[source, ruby]

bad

User.all.find(id) User.all.order(:created_at) users.all.where(id: ids) user.articles.all.order(:created_at)

good

User.find(id) User.order(:created_at) users.where(id: ids) user.articles.order(:created_at)

NOTE: When the receiver for all is an association, there are methods whose behavior changes by omitting all.

The following methods behave differently without all:

• delete - https://api.rubyonrails.org/classes/ActiveRecord/Persistence/ClassMethods.html#method-i-delete[with all] / https://api.rubyonrails.org/classes/ActiveRecord/Associations/CollectionProxy.html#method-i-delete[without all]
• delete_all - https://api.rubyonrails.org/classes/ActiveRecord/Relation.html#method-i-delete_all[with all] / https://api.rubyonrails.org/classes/ActiveRecord/Associations/CollectionProxy.html#method-i-delete_all[without all]
• destroy - https://api.rubyonrails.org/classes/ActiveRecord/Persistence/ClassMethods.html#method-i-destroy[with all] / https://api.rubyonrails.org/classes/ActiveRecord/Associations/CollectionProxy.html#method-i-destroy[without all]
• destroy_all - https://api.rubyonrails.org/classes/ActiveRecord/Relation.html#method-i-destroy_all[with all] / https://api.rubyonrails.org/classes/ActiveRecord/Associations/CollectionProxy.html#method-i-destroy_all[without all]

So, when considering removing all from the receiver of these methods, it is recommended to refer to the documentation to understand how the behavior changes.

=== find_by memoization [[find-by-memoization]]

Avoid memoizing find_by results with ||=. find_by may return nil, in which case it will not be memoized as intended.

[source,ruby]

bad

def current_user @current_user ||= User.find_by(id: session[:user_id]) end

good

def current_user return @current_user if defined?(@current_user)

@current_user = User.find_by(id: session[:user_id]) end

== Migrations

=== Schema Version [[schema-version]]

Keep the schema.rb (or structure.sql) under version control.

=== DB Schema Load [[db-schema-load]]

Use rake db:schema:load instead of rake db:migrate to initialize an empty database.

=== Default Migration Values [[default-migration-values]]

Enforce default values in the migrations themselves instead of in the application layer.

[source,ruby]

bad - application enforced default value

class Product < ApplicationRecord def amount self[:amount] || 0 end end

good - database enforced

class AddDefaultAmountToProducts < ActiveRecord::Migration def change change_column_default :products, :amount, 0 end 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.

=== 3-state Boolean [[three-state-boolean]]

With SQL databases, if a boolean column is not given a default value, it will have three possible values: true, false and NULL. Boolean operators https://en.wikipedia.org/wiki/Three-valued_logic[work in unexpected ways] with NULL.

For example in SQL queries, true AND NULL is NULL (not false), true AND NULL OR false is NULL (not false). This can make SQL queries return unexpected results.

To avoid such situations, boolean columns should always have a default value and a NOT NULL constraint.

[source,ruby]

bad - boolean without a default value

add_column :users, :active, :boolean

good - boolean with a default value (false or true) and with restricted NULL

add_column :users, :active, :boolean, default: true, null: false add_column :users, :admin, :boolean, default: false, null: false

=== Foreign Key Constraints [[foreign-key-constraints]]

Enforce foreign-key constraints. As of Rails 4.2, Active Record supports foreign key constraints natively.

[source,ruby]

bad - does not add foreign keys

create_table :comment do |t| t.references :article t.belongs_to :user t.integer :category_id end

good

create_table :comment do |t| t.references :article, foreign_key: true t.belongs_to :user, foreign_key: true t.references :category, foreign_key: { to_table: :comment_categories } end

=== Change vs Up/Down [[change-vs-up-down]]

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

[source,ruby]

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

=== Define Model Class Migrations [[define-model-class-migrations]]

If you have to use models in migrations, make sure you define them so that you don't end up with broken migrations in the future.

[source,ruby]

db/migrate/<migration_file_name>.rb

frozen_string_literal: true

bad

class ModifyDefaultStatusForProducts < ActiveRecord::Migration def change old_status = 'pending_manual_approval' new_status = 'pending_approval'

reversible do |dir|
  dir.up do
    Product.where(status: old_status).update_all(status: new_status)
    change_column :products, :status, :string, default: new_status
  end

  dir.down do
    Product.where(status: new_status).update_all(status: old_status)
    change_column :products, :status, :string, default: old_status
  end
end

end end

good

Define table_name in a custom named class to make sure that you run on the

same table you had during the creation of the migration.

In future if you override the Product class and change the table_name,

it won't break the migration or cause serious data corruption.

class MigrationProduct < ActiveRecord::Base self.table_name = :products end

class ModifyDefaultStatusForProducts < ActiveRecord::Migration def change old_status = 'pending_manual_approval' new_status = 'pending_approval'

reversible do |dir|
  dir.up do
    MigrationProduct.where(status: old_status).update_all(status: new_status)
    change_column :products, :status, :string, default: new_status
  end

  dir.down do
    MigrationProduct.where(status: new_status).update_all(status: old_status)
    change_column :products, :status, :string, default: old_status
  end
end

end end

=== Meaningful Foreign Key Naming [[meaningful-foreign-key-naming]]

Name your foreign keys explicitly instead of relying on Rails auto-generated FK names. (https://guides.rubyonrails.org/active_record_migrations.html#foreign-keys)

[source,ruby]

bad

class AddFkArticlesToAuthors < ActiveRecord::Migration def change add_foreign_key :articles, :authors end end

good

class AddFkArticlesToAuthors < ActiveRecord::Migration def change add_foreign_key :articles, :authors, name: :articles_author_id_fk end end

=== Reversible Migration [[reversible-migration]]

Don't use non-reversible migration commands in the change method. Reversible migration commands are listed below. https://api.rubyonrails.org/classes/ActiveRecord/Migration/CommandRecorder.html[ActiveRecord::Migration::CommandRecorder]

[source,ruby]

bad

class DropUsers < ActiveRecord::Migration def change drop_table :users end end

good

class DropUsers < ActiveRecord::Migration def up drop_table :users end

def down create_table :users do |t| t.string :name end end end

good

In this case, block will be used by create_table in rollback

https://api.rubyonrails.org/classes/ActiveRecord/ConnectionAdapters.html#method-i-drop_table

class DropUsers < ActiveRecord::Migration def change drop_table :users do |t| t.string :name end end end

== Views

=== No Direct Model View [[no-direct-model-view]]

Never call the model layer directly from a view.

=== No Complex View Formatting [[no-complex-view-formatting]]

Avoid complex formatting in the views. A view helper is useful for simple cases, but if it's more complex then consider using a decorator or presenter.

=== Partials [[partials]]

Mitigate code duplication by using partial templates and layouts.

=== No Instance Variables in Partials [[no-instance-variables-in-partials]]

Avoid using instance variables in partials, pass a local variable to render instead. The partial may be used in a different controller or action, where the variable can have a different name or even be absent. In these cases, an undefined instance variable will not raise an exception whereas a local variable will.

[source,erb]

<%= render 'course_description' %>

<%= @course.description %>

<%= render 'course_description', course: @course %>

<%= course.description %>

== Internationalization

=== Locale Texts [[locale-texts]]

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.

=== Translated Labels [[translated-labels]]

When the labels of an Active Record model need to be translated, use the activerecord scope:

---

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.

=== Organize Locale Files [[organize-locale-files]]

Separate the texts used in the views from translations of Active Record attributes. Place the locale files for the models in a folder locales/models and the texts used in the views in folder locales/views.

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.

[source,ruby]

config/application.rb

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

=== Shared Localization [[shared-localization]]

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

=== Short I18n [[short-i18n]]

Use the short form of the I18n methods: I18n.t instead of I18n.translate and I18n.l instead of I18n.localize.

=== Lazy Lookup [[lazy-lookup]]

Use "lazy" lookup for locale entries from views and controllers. Let's say we have the following structure:

---

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:

[source,ruby]

bad

= t 'users.show.title'

good

= t '.title'

=== Dot-separated Keys [[dot-separated-keys]]

Use dot-separated locale keys instead of specifying the :scope option with an array or a single symbol. Dot-separated notation is easier to read and trace the hierarchy.

[source,ruby]

bad

I18n.t :record_invalid, scope: [:activerecord, :errors, :messages]

good

I18n.t :record_invalid, scope: 'activerecord.errors.messages' I18n.t 'activerecord.errors.messages.record_invalid'

bad

I18n.t :title, scope: :invitation

good

I18n.t 'title.invitation'

=== I18n Guides [[i18n-guides]]

More detailed information about the Rails I18n can be found in the https://guides.rubyonrails.org/i18n.html[Rails Guides]

== Assets

Use the https://guides.rubyonrails.org/asset_pipeline.html[asset pipeline] to leverage organization within your application.

=== Reserve app/assets [[reserve-app-assets]]

Reserve app/assets for custom stylesheets, javascripts, or images.

=== lib/assets [[lib-assets]]

Use lib/assets for your own libraries that don't really fit into the scope of the application.

=== vendor/assets [[vendor-assets]]

Third party code such as https://jquery.com/[jQuery] or https://twitter.github.com/bootstrap/[bootstrap] should be placed in vendor/assets.

=== gem/assets [[gem-assets]]

When possible, use gemified versions of assets (e.g. https://github.com/rails/jquery-rails[jquery-rails], https://github.com/joliss/jquery-ui-rails[jquery-ui-rails], https://github.com/thomas-mcdonald/bootstrap-sass[bootstrap-sass], https://github.com/zurb/foundation[zurb-foundation]).

== Mailers

=== Mailer Name [[mailer-name]]

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.

=== HTML Plain Email [[html-plain-email]]

Provide both HTML and plain-text view templates.

=== Enable Delivery Errors [[enable-delivery-errors]]

Enable errors raised on failed mail delivery in your development environment. The errors are disabled by default.

[source,ruby]

config/environments/development.rb

config.action_mailer.raise_delivery_errors = true

=== Local SMTP [[local-smtp]]

Use a local SMTP server like https://github.com/sj26/mailcatcher[Mailcatcher] in development environment.

[source,ruby]

config/environments/development.rb

config.action_mailer.smtp_settings = { address: 'localhost', port: 1025,

more settings

}

=== Default Hostname [[default-hostname]]

Provide default settings for the host name.

[source,ruby]

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'

=== Email Addresses [[email-addresses]]

Format the from and to addresses properly. Use the following format:

[source,ruby]

in your mailer class

default from: 'Your Name <info@your_site.com>'

If you're using Rails 6.1 or higher, you can use the email_address_with_name method:

[source,ruby]

in your mailer class

default from: email_address_with_name('info@your_site.com', 'Your Name')

=== Delivery Method Test [[delivery-method-test]]

Make sure that the e-mail delivery method for your test environment is set to test:

[source,ruby]

config/environments/test.rb

config.action_mailer.delivery_method = :test

=== Delivery Method SMTP [[delivery-method-smtp]]

The delivery method for development and production should be smtp:

[source,ruby]

config/environments/development.rb, config/environments/production.rb

config.action_mailer.delivery_method = :smtp

=== Inline Email Styles [[inline-email-styles]]

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: https://github.com/fphilipe/premailer-rails[premailer-rails] and https://github.com/Mange/roadie[roadie].

=== Background Email [[background-email]]

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 https://github.com/mperham/sidekiq[sidekiq] gem.

== Active Support Core Extensions

=== try! [[try-bang]]

Prefer Ruby 2.3's safe navigation operator &. over ActiveSupport#try!.

[source,ruby]

bad

obj.try! :fly

good

obj&.fly

=== Active Support Aliases [[active_support_aliases]]

Prefer Ruby's Standard Library methods over ActiveSupport aliases.

[source,ruby]

bad

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

good

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

=== Active Support Extensions [[active_support_extensions]]

Prefer Ruby's Standard Library over uncommon Active Support extensions.

[source,ruby]

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'

=== inquiry [[inquiry]]

Prefer Ruby's comparison operators over Active Support's Array#inquiry, and String#inquiry.

[source,ruby]

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'

=== exclude? [[exclude]]

Prefer Active Support's exclude? over Ruby's negated include?.

[source,ruby]

bad

!array.include?(2) !hash.include?(:key) !string.include?('substring')

good

array.exclude?(2) hash.exclude?(:key) string.exclude?('substring')

=== Prefer using squiggly heredoc over strip_heredoc [[prefer-squiggly-heredoc]]

If you're using Ruby 2.3 or higher, prefer squiggly heredoc (<<~) over Active Support's strip_heredoc.

[source,ruby]

bad

<<EOS.strip_heredoc some text EOS

bad

<<-EOS.strip_heredoc some text EOS

good

<<~EOS some text EOS

=== Prefer to_fs for Formatted Strings [[prefer-to-fs]]

If you're using Rails 7.0 or higher, prefer to_fs over to_formatted_s. to_formatted_s is just too cumbersome for a method used that frequently.

[source,ruby]

bad

time.to_formatted_s(:db) date.to_formatted_s(:db) datetime.to_formatted_s(:db) 42.to_formatted_s(:human)

good

time.to_fs(:db) date.to_fs(:db) datetime.to_fs(:db) 42.to_fs(:human)

== Time

=== Time Zone Config [[tz-config]]

Configure your timezone accordingly in application.rb.

[source,ruby]

config.time_zone = 'Eastern European Time'

optional - note it can be only :utc or :local (default is :utc)

config.active_record.default_timezone = :local

=== Time.parse [[time-parse]]

Don't use Time.parse.

[source,ruby]

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

=== to_time [[to-time]]

Don't use https://api.rubyonrails.org/classes/String.html#method-i-to_time[`String#to_time`]

[source,ruby]

bad - assumes time string given is in the system's time zone.

'2015-03-02 19:05:37'.to_time

good

Time.zone.parse('2015-03-02 19:05:37') # => Mon, 02 Mar 2015 19:05:37 EET +02:00

=== Time.now [[time-now]]

Don't use Time.now.

[source,ruby]

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.

=== Prefer all_(day|week|month|quarter|year) over range of date/time [[date-time-range]]

Prefer all_(day|week|month|quarter|year) over beginning_of_(day|week|month|quarter|year)..end_of_(day|week|month|quarter|year) to get the range of date/time.

[source,ruby]

bad

date.beginning_of_day..date.end_of_day date.beginning_of_week..date.end_of_week date.beginning_of_month..date.end_of_month date.beginning_of_quarter..date.end_of_quarter date.beginning_of_year..date.end_of_year

good

date.all_day date.all_week date.all_month date.all_quarter date.all_year

== Duration

=== Duration Application

If used without a parameter, prefer from_now and ago instead of since, after, until or before.

[source,ruby]

bad - It's not clear that the qualifier refers to the current time (which is the default parameter)

5.hours.since 5.hours.after 5.hours.before 5.hours.until

good

5.hours.from_now 5.hours.ago

If used with a parameter, prefer since, after, until or before instead of from_now and ago.

[source,ruby]

bad - It's confusing and misleading to read

2.days.from_now(yesterday) 2.days.ago(yesterday)

good

2.days.since(yesterday) 2.days.after(yesterday) 2.days.before(yesterday) 2.days.until(yesterday)

Avoid using negative numbers for the duration subject. Always prefer using a qualifier that allows using positive literal numbers.

[source,ruby]

bad - It's confusing and misleading to read

-5.hours.from_now -5.hours.ago

good

5.hours.ago 5.hours.from_now

=== Duration Arithmetic

Use Duration methods instead of adding and subtracting with the current time.

[source,ruby]

bad

Time.current - 1.minute Time.zone.now + 2.days

good

1.minute.ago 2.days.from_now

== Bundler

=== Dev/Test Gems [[dev-test-gems]]

Put gems used only for development or testing in the appropriate group in the Gemfile.

=== Only Good Gems [[only-good-gems]]

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.

=== Gemfile.lock [[gemfile-lock]]

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.

== Testing

=== Integration Testing

Prefer integration style controller tests over functional style controller tests, https://api.rubyonrails.org/v7.0.0/classes/ActionController/TestCase.html[as recommended in the Rails documentation].

[source,ruby]

bad

class MyControllerTest < ActionController::TestCase end

good

class MyControllerTest < ActionDispatch::IntegrationTest end

=== freeze_time [[freeze-time]]

Prefer https://api.rubyonrails.org/classes/ActiveSupport/Testing/TimeHelpers.html#method-i-freeze_time[ActiveSupport::Testing::TimeHelpers#freeze_time] over https://api.rubyonrails.org/classes/ActiveSupport/Testing/TimeHelpers.html#method-i-travel_to[ActiveSupport::Testing::TimeHelpers#travel_to] with an argument of the current time.

[source,ruby]

bad

travel_to(Time.now) travel_to(DateTime.now) travel_to(Time.current) travel_to(Time.zone.now) travel_to(Time.now.in_time_zone) travel_to(Time.current.to_time)

good

freeze_time

== Managing Processes

=== Foreman [[foreman]]

If your projects depends on various external processes use https://github.com/ddollar/foreman[foreman] to manage them.

== Further Reading

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

• https://www.informit.com/store/rails-5-way-9780134657677[The Rails 5 Way]
• https://guides.rubyonrails.org/[Ruby on Rails Guides]
• https://pragprog.com/titles/rspec3/effective-testing-with-rspec-3/[Effective Testing with RSpec 3]
• https://pragprog.com/titles/hwcuc2/the-cucumber-book-second-edition/[The Cucumber Book]
• https://leanpub.com/everydayrailsrspec[Everyday Rails Testing with RSpec]
• https://pragprog.com/titles/nrtest3/rails-5-test-prescriptions/[Rails 5 Test Prescriptions]
• https://rspec.rubystyle.guide[RSpec Style Guide]

== 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 https://www.patreon.com/bbatsov[Patreon].

=== How to Contribute?

It's easy, just follow the contribution guidelines below:

• https://help.github.com/articles/fork-a-repo[Fork] the https://github.com/rubocop/rails-style-guide[project] on GitHub
• Make your feature addition or bug fix in a feature branch.
• Include a http://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html[good description] of your changes
• Push your feature branch to GitHub
• Send a https://help.github.com/articles/using-pull-requests[Pull Request]

== License

image:https://i.creativecommons.org/l/by/3.0/88x31.png[Creative Commons License] This work is licensed under a https://creativecommons.org/licenses/by/3.0/deed.en_US[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, + https://twitter.com/bbatsov[Bozhidar]