money gem: inherit currency from parent model

Can someone tell me how to inherit the currency from a parent model?

I use the money gem (https://github.com/RubyMoney/money) and have 2 models (market and tradelimit).

The price of the market becomes updated periodical and if there is a tradelimit which has the same price, the user becomes informed.

Because the market has already the currency stored, i dont want to store it again in the tradelimit model (not dry):

class Market << AR
  composed_of :price,
    :class_name => "Money"开发者_Python百科,
    :mapping => [%w(price_cents cents), %w(currency currency_as_string)],
    :constructor => Proc.new { |cents, currency| Money.new(cents || 0, currency || 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

#tradelimit.rb

class Tradelimit << AR
  composed_of :price,
    :class_name => "Money",
    :mapping => [%w(price_cents cents), %w(currency currency_as_string)],
    :constructor => Proc.new { |cents, currency| Money.new(cents || 0, currency || 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

How can I inherit now the currency from the parent (market) model? I tried to override the currency method in the tradelimit model, but this doenst work..

Any suggestions? Thanks!

EDIT:

Or is there a way (without the composed_of feature) to provide this functionality?

Have you tried:

class Market < AR
  #use Money as a mixin
  include Money
...

end

#Now Tradelimit should inherit all from Market
class Tradelimit <  Market