Rails money gem and form builder

Question

I'm having an issue with the forms and the money gem.

This is my problem:

1. I create a record which has an "amount" field (mapped to money object). Let's say I enter 10 (dollars).
2. The money gem converts it to 1000 (cents)
3. I edit the same record and the form pre-populates the amount field as 1000
4. If I save the record without changing anything, it will convert the 1000 (dollars) to 100000 (cents)

How do I make it display the pre-populated amount in dollars instead of cents?

Edit:

I tried editing the _form.html like this:

= f.text_field(:amount, :to_money)

and I get this error:

undefined method `merge' for :to_money:Symbol

Answer 1

Given a migration as follows:

class CreateItems < ActiveRecord::Migration
  def self.up
    create_table :items do |t|
      t.integer :cents
      t.string :currency
      t.timestamps
    end
  end

  def self.down
    drop_table :items
  end
end

And a model as follows:

class Item < ActiveRecord::Base
  composed_of :amount,
    :class_name  => "Money",
    :mapping     => [%w(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 conver #{value.class} to Money") }
end

Then this form code should work perfectly (I just tested under Rails 3.0.3), properly displaying and saving the dollar amount every time you save/edit. (This is using the default scaffold update/create methods).

<%= form_for(@item) do |f| %>
  <div class="field">
    <%= f.label :amount %><br />
    <%= f.text_field :amount %>
  </div>
  <div class="actions">
    <%= f.submit %>
  </div>
<% end %>

Answer 2

If you have multiple money fields in your table and you can't name them all "cents".

class CreateItems < ActiveRecord::Migration
  def self.up
    create_table :items do |t|
      t.integer :purchase_price_cents
      t.string :currency
      t.timestamps
    end
  end

  def self.down
    drop_table :items
  end
end

which would change your model to

class Item < ActiveRecord::Base

  composed_of :purchase_price,
    :class_name  => "Money",
    :mapping     => [%w(purchase_price_cents cents), %w(currency currency_as_string)],
    :constructor => Proc.new { |purchase_price_cents, currency| Money.new(purchase_price_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