How can I format the value shown in a Rails edit field?

Question

I would like to make editing form fields as user-friendly as possible. For example, for numeric values, I would like the field to be displayed with commas (like number

Answer 1

You can use the number_format plugin. By specifying a number_format for an existing numeric attribute inside your model, the attribute will now appear as formatted to Rails in all forms and views. It will also be parsed back from that format (when assigned via forms) prior to insertion into the database. (The plugin also creates purely numeric unformatted_ accessors which can continue to be used for arithmetic, or for direct numerical assignment or retrieval by you for seamless integration.)

class MyModel < ActiveRecord::Base
  # this model has the balance attribute, which we
  #  want to display using formatting in views,
  #  although it is stored as a numeric in the database
  number_format :balance, 
                :precision => 2,
                :delimiter => ',',
                :strip_trailing_zeros => false

  def increment_balance
    unformatted_balance += 10
  end

You can also combine the above with a Javascript solution, which can force the user to maintain the decimal point and thousands separators in place while editing, although this is really not necessary.