Question

I am using Ruby on Rails v3.2.2 and I would like to know if it is a valid approach to state a Active Record Association in a mixin module. Why?

More:

1. what are advantages and disadvantages of this approach?
2. is there something to which I should pay attention to?
3. is there some prescription to make that?

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Note: I would like to DRY (Don’t Repeat Yourself) my code since statements related to my Active Record Associations are the same for multiple models.

Answer 1

Go ahead and do it! Regarding your questions:

• Regarding 1: The biggest advantage is that you have a clean code base with no duplicated code; the biggest disadvantage I can think of is that it might not be instantly obvious to someone looking through your code.

• Regarding 3: You have to define the associations either in the included callback or using the new ActiveSupport::Concern extensions for it.

Example:

# using the standard include callback
module LocationAwareness

  def self.included(base)
    base.has_one :location
  end
end

or

# using ActiveSupport::Concern
module LocationAwareness
  extend ActiveSupport::Concern

  included do
    base.has_one :location
  end
end

then you can use it in your models like that:

class Person < ActiveRecord::Base
  include LocationAwareness
end

class Gig < ActiveRecord::Base
  include LocationAwareness
end

#...

This approach of course starts to make even more sense if you have more shared behaviour than “just” the association…