Question

I have a model called Vote and this is what vote.rb looks like:

class Vote < ActiveRecord::Base
  belongs_to :votable, :polymorphic => true
  belongs_to :user

  before_create :update_total

  protected

  def update_total
    self.total ||= 0
    self.total += self.polarity
  end
end

(it is polymorphic because it also belongs to another model called Comment).

Each time a vote is created the value of total is updated. For example, Vote.create(:polarity => 2), will produce :polarity => 2, :total => 2

I just realize that this doesn’t make sense because :polarity will always equal to :total. What I actually want to do is to have the total to the model that Vote belongs to; in this case Post and Comment (Vote belongs to post and Post has many votes) so that each time a vote is created, the total column in the post will be updated. Like this:

May 13

Post.total = 3 (:id => 2)

Vote.polarity = 1 (:id => 1)
Vote.polarity = -1 (:id => 2)
Vote.polarity = 3 (:id => 3)

May 14

Post.total = 4 (:id => 2)

Vote.polarity = 1 (:id => 1)
Vote.polarity = -1 (:id => 2)
Vote.polarity = 3 (:id => 3)
Vote.polarity = 1 (:id => 4)

Answer 1

You need to update the total of the votable object in this way:

def update_total
  if self.votable.class.column_names.include?("total")
    total_average = self.votable.total ||= 0
    self.votable.update_attribute(:total, total_average + self.polarity)
  end
end

or you can use the conditional callback like @Sandip says:

before_create :update_total, :if => defined_total

def defined_total
  self.votable.class.column_names.include?("total")
end

def update_total
  total_average = self.votable.total ||= 0
  self.votable.update_attribute(:total, total_average + self.polarity)
end