Where to put a function called by a model?


Any classes/modules you add to your app/model or lib directories are
accessible from any of your models (and your controllers and views).
So you could add a class like this:

Class DateToolbox
   def self.convert_date(d)

Then from any model you can call DateToolbox.convert_date.

A slightly more complicated but cleaner approach would be to override
or augment the simple_date_select plugin with your conversion
routine. Here is a simple example of adding a method to Ruby's built-
in String class:

class String
   def hello
     "hello #{self.to_s}"

"aaron".hello => hello aaron