Rails 3. How to explicitly round a number to two decimal places in the model? [duplicate]

Answer 1

You can simply use x.round(2) when displaying the number - that will always display two decimal places. It's generally recommended to store prices as integers in the backend database because they are handled better when you need a really high level of precision. In this case though, you can choose to go either way.

Answer 2

If it's a :float or :decimal, 80 and 80.00 in Ruby are going to be the same thing (as will 80.0000). The latter isn't "stored" with more decimal places, and trailing zeroes only make sense in the view. You can use sprintf like you said, or you can use Rails' handy number_with_precision helper:

<%= number_with_precision price, :precision => 2 %>

Here's another SO question on this topic, by the way. @Matthew Rudy is right about one thing: For money columns you should be using :decimal.

If you're really committed to not having this in your view, you could use something like Draper to apply decorators to your attributes (which will merely move your number_with_precision call out of the way and into a new Decorator class), but it's probably overkill in this instance.

Answer 3

You should try using the :decimal type of database field, with the :scale set to 2

To add a decimal column to a new table;

create_table :my_table do |t|
  t.decimal :my_column, :scale => 2
end

To add a column to an existing table;

add_column :my_table, :my_column, :decimal, :scale => 2

It is wise to have precisions since some database does not have precision defaults. Such as postgresql:

 add_column :my_table, my_column, precision: 30, scale: 2

Answer 4

For this I use the number_to_currency formater. Since I am in the US the defaults work fine for me.

<% price = 45.9999 %>
<price><%= number_to_currency(price)%></price>
=> <price>$45.99</price>

You can also pass in options if the defaults don't work for you. Documentation on available options at api.rubyonrails.org