Business rule validation

user.rb

# CREATE TABLE users (id INT  NOT NULL AUTO_INCREMENT, age INT UNSIGNED, PRIMARY KEY id)

class User < ActiveRecord::Base
  # column gives us age / age=
  validates :age, presence: true, may_serve_alcohol: true
end

class MayServeAlcoholValidator < ActiveModel::EachValidator
  def validate_each(model, attribute, value)
    if model[attribute].present? && model[attribute] < 18
      model.errors.add attribute, "must be over 18 to serve as bar staff"
    end
  end
end