Rails model template

model_template.rb

class ContractLink < ActiveRecord::Base
  # NOTE: whenever possible, use alphabetic order
  
  # includes/extends
  # --
  include MyModule
  extend MyOtherModule
  
  # class definitions, like gem configurations/initializations
  # --
  # example, if using paper_trail gem
  has_paper_trail
  # kaminari (pagination)
  paginates_per 20
  
  # constant definitions
  # --
  CONSTANT_TYPES = [:one, :two, :other]
  MIN_PROFIT = 30_000
  STATUSES = { ready: 1, scheduled: 2, running: 3, success: 4, failure: 5 }
  
  
  # callbacks (order: http://api.rubyonrails.org/classes/ActiveRecord/Callbacks.html)
  # --
  after_initialize :defaults, if: :new_record?
  after_commit :notify
  
  # associations, grouped by "kind" (belongs_to, has_one, has_many...) in a "priority" order (belongs, one, many)
  # --
  # NOTE: :some before :that because of alphabetical order
  belongs_to :some
  belongs_to :that
  
  has_one :thing
  
  has_many :tags
  
  
  # attributes section
  # --
  #   rails version 3.x
  attribute_accessible :description, :income, :kind, :name, 
                       :status, :that_attributes
  # enum: rails >= 4.1 (http://edgeapi.rubyonrails.org/classes/ActiveRecord/Enum.html)
  enum status: STATUSES
  
  # nested attrs
  accepts_nested_attributes_for :that, allow_destroy: true
  
  # validations section
  # --
  # NOTE: Order validations by attribute/association name.
  #
  # NOTE2: Let's try to use one `validates` per attribute, so we can easily
  #   check what's been validates for each attribute.
  #
  # wrong:
  #   validates_uniqueness_of :name
  #   validates_presence_of :name
  #
  # right:
  #   validates :name, presence: true, uniqueness: true
  #
  
  validates :income, numericality: { greater_than_or_equal_to: 0 }
  validates :kind, numericality: { only_integer: true, 
                     greater_than_or_equal_to: 0,
                     less_than: CONSTANT_TYPES.size }
  validates :name, presence: true, uniqueness: true
  # Association presence is validated through association name (not association_id attribute!)                    
  validates :some, presence: true
  # IMPORTANT: this is not necessary if using `enum` (rails 4.1+)
  validates :status, in: STATUSES.values
                  
  # custom validations
  validate :special_check
                    
  # associated models with nested attributes
  validates_associated :that
  
  
  # class methods (like scopes)
  def self.special
    where(kind: 'special')
  end
  
  
  # instance methods
  def positive?
    income > MIN_PROFIT
  end
  
  
  # private stuff (two lines separating it)
  private
  
  # Almost all callback method should be private.
  # That's true for custom validation methods too.
  
  def defaults
    # this method will run for newly initialized records.
    # it can be used to set default values.
    self.status ||= :ready
  end
  
  def notify
    send_income_changed_message_to(Person.managers) if income_changed?
    send_something_else_to(Person.project_leaders)
  end
  
  def special_check
    # note that this error message get's automatically translated to
    # activerecord.errors.models.contract_link.attributes.that.invalid (if defined)
    #  falling back to default activerecord.errors.invalid ('is not valid').
    errors.add(:that, :invalid) unless that.active?
  end
  
end