Rails - Jun 2008 - Suggestions for adding a new abstract data type to AR using a composed_of

Hello everybody,

I had been searching the web but I can’t find a way to add a new
abstract data type to AR using a composed_of. To put this in context
let me explain what I want to do:
In a rails app I had developed a Money Class that use to
attr :amount, :currency. I had add functionality to have Factories for
creating Money in different currencies, arithmetical operations,
comparisons, and several financial calculations (interest, expected
values, amortized payments, etc.) . I had been using this in my models
as

composed_of :price_money,
            :class_name => Money,
            :mapping =>
                [ # database ruby
                [ :price, :amount ],
                [ :currency, :currency ]
            ]

I have also a Bank Class were I kept the exchange rates among
currencies
After talking in RailsConf2008 with several railers they told me that
will be good if I can deploy this as a plugin or a gem. I had been
working in extracting this as a plugin, but I would like to be able to
add a new abstract data type to AR for money, then we can use in
migrations something like this as example:

  create_table "prices", :force => true do |t|
    t.money  "price", :precision => 16, :scale => 4.
:default_currency
=> "USD"
  end

Rather than

  create_table "prices", :force => true do |t|
    t.decimal  "price", :precision => 16, :scale => 4
    t.string   "currency", :limit => 3, :default =>
"USD", :null =>
false
  end

And get out also the need for the composed_of declaration.

I will appreciate very much any suggestion how to tackle this.

Best regards,

Manuel Vidaurre

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