raise "ActiveRecord needs to be already required" unless defined?(ActiveRecord::Base)

class ActiveRecord::Base
  # Convenience wrapper around ActiveRecord's composed_of method for Money attributes that need to be persisted.
  #
  # @param [Array of Symbols]
  # @example
  #   composed_of_money :unit_price
  #   composed_of_money :unit_price, :total_price
  def self.composed_of_money(*fields)
    fields.each do |field|
      composed_of field,
                  :class_name => "Money",
                  :mapping => [[field, "amount"]],
                  :constructor => Proc.new { |amount| Money.new(amount || 0, Money.default_currency) },
                  :converter => Proc.new { |value| value.respond_to?(:to_money) ? value.to_money : raise(ArgumentError, "Can't convert #{value.class} to Money") }
    end
  end
end