Skinny Controllers and Overweight Models
17 Aug, 2008
2 minute read

All Rails developers know the slogan “Skinny Controllers, Fat Models” and I heartily agree with it. Every conference you go to, you hear it. But there’s a problem! My Fat models got overweight!

What happened? By stuffing all applications logic in the Models, they become fat, very fat. Although this is supposed to be a good thing, I don’t like it. My models get so fat that it takes me forever to scroll through it and find the method I’m working on. There must be a better way!

Well, yes there is: create modules! Normally you’d write a module to reuse your code in different places, but there’s no rule that says you may not use a module only once.

So, I package all related code (e.g. Authentication, state management, managing associated objects, etc) into different modules and place them in the /lib directory. Let’s say you have a a bunch of methods to handle keep a counter on your User model

class User < ActiveRecord::Base
  attr_accessor :counter

  def up
    counter += 1
  end

  def down
    counter -= 1
  end

  def reset
    counter = 0
  end
end

You could create a new file lib/counter.rb and include that module in your User model.

class User < ActiveRecord::Base
  attr_accessor :counter
  include Counter
end

module Counter
  def up
    counter += 1
  end

  def down
    counter -= 1
  end

  def reset
    counter = 0
  end
end

As you can see, this keeps your fat User model clean and makes it easier for you to find code that applies to a certain function.