defaults.rb

module Defaults
  extend ActiveSupport::Concern

  included do
    # Make sure #set_default_values is called after initialize
    after_initialize :set_default_values

    # Set default values before initialize
    def set_default_values
      self.class.defaults.each do |attribute, param|
        next if self.send(attribute).present?
        value = param.respond_to?(:call) ? param.call(self) : param
        self.send(:write_attribute, attribute, value) if self
      end
    end
  end

  module ClassMethods
    # Store defaults
    @@defaults = {}

    # Set a default value
    #
    # @param [Symbol] Attribute
    # @param [Mixed] Default value
    def default(attribute, value = nil, &block)
      @@defaults[attribute] = value || block
    end

    # Get default attributes
    #
    # @return [Hash]
    def defaults
      @@defaults
    end
  end
end