Rails money gem and form builder - ruby-on-rails

Question

I'm having an issue with the forms and the money gem.
This is my problem:
I create a record which has an "amount" field (mapped to money object). Let's say I enter 10 (dollars).
The money gem converts it to 1000 (cents)
I edit the same record and the form pre-populates the amount field as 1000
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

You can now edit monetized fields directly (money-rails 1.3.0):
# add migration
add_column :products, :price, :price_cents
# set monetize for this field inside the model
class Product
monetize :price_cents
end
# inside form use .price instead of .price_cents method
f.text_field :price
See https://stackoverflow.com/a/30763084/46039

Answer 3

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

Answer 4

monetizing and the simple form, the steps as follows:
Migration
add_monetize :table, :amount
Model with validation
monetize :amount_cents, allow_nil: true, numericality: {greater_than: 0}
Controller permit params (dont use amount_cents here)
params.require(:model).permit(:amount)
simple form input
when it's saved it will be saved in cents in amount_cents column in db