Not Only… But Also

The Rails ‘fat model’ pattern is a good one but can result in very large model classes. It can be unwieldy to work in such files as they begin to look a bit messy. Assuming you have judiciously appraised the model for opportunities to extract out pieces into libraries, it still may leave you with a lot of code. I find this is particularly the case for validations for models with a large number of columns.

This is where allowing for multiple files to define a class can help and is what NotOnlyButAlso does. It defines a convention to help organise multiple files as well as avoiding the need for repititive code when using modules as containers or re-opening the classes.

You might recognise this style of solution as used by the concerned_with plugin (github.com/jakehow/concerned_with/). I wrote this a long time ago before I knew of the concerned_with plugin. I have released it because its got a simpler interface and I love the name.

For interest here are some discussions of this type of solution in regards to concerned_with:

m.onkey.org/2008/9/15/active-record-tips-and-tricks

paulbarry.com/articles/2008/08/30/concerned-with-skinny-controller-skinny-model

For extra credit:

en.wikipedia.org/wiki/Not_Only..._But_Also

Install

From Gemcutter:

  gem install not_only_but_also

Or as plugin:

  ./script/install plugin git://github.com/adzap/not_only_but_also.git

Usage

For example you want to extract out the validations to a separate file:

  class Post
    not_only_but_also :validations
  end

  # in app/models/post/validations.rb

  Post.not_only_but_also do
    validates_presence_of :title
  end

OR the shorthand version:

  class Post
    also_has :validations
  end

  # in app/models/post/validations.rb

  Post.also_has do
    validates_presence_of :title
  end

There is a generator for quickly creating the context file and the directory if need be

  ./script/generate not_only_but_also Post validations

Adding the context to the model to have it loaded is left for as an exercise for the developer.

Copyright © 2009 Adam Meehan, released under the MIT license