What is the correct order of associations, scopes, validations, etc. in Rails models

Question

Edited this old question to include an answer from below: Rubocop has it https://github.com/rubocop-hq/rails-style-guide#macro-style-methods

Rails is all about 'Convention over Configuration'. However, I haven't come across a 'standard' for the order of associations, scopes, includes, validations, ... in Rails models yet. Take for example the following, simplified, product model:

class Product < ActiveRecord::Base
  mount_uploader :logo, AssetUploader
  acts_as_taggable
  paginates_per 50

  include ActionView::Helpers::NumberHelper

  belongs_to :company

  validates_presence_of [:title, :price, :plu]

  scope :on_website, where(display: true)

  def display_price
    ...
  end
end

Is this the correct order? It's maybe not that important to many people, but I personally think it would be great if there were a convention on this.

Answer 1

Rubocop has it https://github.com/rubocop-hq/rails-style-guide#macro-style-methods

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

  # Rails 4+ enums after attr macros
  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