DRY model code

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I had a case in my postit application where I needed to add voting for both comments and posts. This required some code in my models for Post and Comment to count the votes:

has_many :votes, as: :voteable

def total_votes
  up_votes - down_votes
end

def up_votes
  self.votes.where(vote: true).size
end

def down_votes
  self.votes.where(vote: false).size
end

This was repeated code in both models that I wanted to DRY up, so after some help from a friend I added this code in a module in the concerns folder under models:

module ActsAsVoteable

  #self.included is called when this module is included in a model
  def self.included(base)
    #class_eval allows me to define methods at runtime within the model that this module is include in
    #class_eval is useful when the class I want to add methods to is not known until runtime. 
    base.class_eval do
      has_many :votes, as: :voteable
    end
  end

  def total_votes
    up_votes - down_votes
  end

  def up_votes
    self.votes.where(vote: true).size
  end

  def down_votes
    self.votes.where(vote: false).size
  end

end

and then in the Post and Comment model all I had to do was add include ActsAsVoteable.

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