Intro to dynamic Rails functions and modules

Preamble

First of all, let me go on record as saying this may not be the proper “Rails” way to do this. This example is a solution that worked well for me, and I’m going to be posting about what I learned from the experience. If anyone has better ways of handling situations like this, please post in the comments. Thanks!

Problem

I wanted to create a Rails module that I could include in various models that would do the same thing. In my case, I wanted to be able to identify fields on that model that, when stored, should strip all non-digits. The practical use of this is storing a phone number. This module would allow the user to enter “(123) 456-7890″ into a form and ActiveRecord to store “1234567890″ as an integer.

The end state should look like:

include NondigitStrip
 
class Contact < ActiveRecord::Base
  strips_nondigits :phone, :fax
end

Solution

A module is a file that gets mixed into models (or other files, I suppose) so that you don’t have to re-write the same code for multiple models that should share the same functions. In this case, I created nondigit_strip.rb and stuck it in my ./lib folder. I’m going to paste the text below, and then explain what it’s doing.

module NondigitStrip
  def strips_nondigits(*attr_names)
    attr_names.each do |attr_name|
      create_strip_method(attr_name) do |org_method, args, block|
        org_method.call(*args, &block)
      end
    end
  end
 
  def create_strip_method(param)
    define_method param.to_s+"=" do |input|
      super(input.gsub(/[^0-9]/,""))
    end
  end
end

There are two methods above. The first one is directly included in the model with strips_nondigits. It takes in a dynamically sized list of attributes (in this case two: :phone and :fax). It then calls the second method which actually creates the digit-stripping method for each attribute.

The second method simply defines a method called param.to_s+”=” (which ends up in the form of phone=) and uses the gsub method of a string to eliminate non-digits. That gsub line can obviously be modified to alter the inputs however you’d need them be. This results in meta-methods (not quite sure what the term is) that look like:

def phone=(input)
  super(input.gsub(/[^0-9]/,""))
end
 
def fax=(input)
  super(input.gsub(/[^0-9]/,""))
end

And… voila! Now you can do things like:

>> c = Contact.new(:phone => "(123) 456-7890").phone
=> 1234567890