Aggregation: problem with uninitialized composed_of object

Hi,

I'm getting this error:

p = Plan.new
p.amount

TypeError: wrong argument type String (expected Fixnum)

Apparently this happens because the aggregation isn't initialized.
Here's the code:

class Plan < ActiveRecord::Base
    composed_of :amount,
              :class_name => "Money",
              :converter => Proc.new { |s| Money.new(s) },
              :mapping => [:price, :value]
end

class Money
  attr_reader :value

  def initialize(string)
    @value = BigDecimal(string.sub(/,/, '.'))
  end

  def to_s
    Integer(@value * 100).to_s.sub(/(\d{2})$/, ',\1')
  end
end

I would like to hide the aggregation from controllers...

There's the after_initialization callback where I could (try to)
initialize the value object if it is nil...

I wonder what's the proper way to deal with this situation?

Thanks,

For the record...

TypeError: wrong argument type String (expected Fixnum)

[snip]

def initialize(string)
@value = BigDecimal(string.sub(/,/, '.'))
end

The problem was that value object can be initialized with a string
(from the form) or with a number (from the db). Thus initialize should
be changed, eg:

def initialize(value)
  @value = BigDecimal(value.to_s(/,/, '.'))
end