Question

I have a Post model that has a polymorphic association with a Vote model:

post.rb:

class Post < ActiveRecord::Base
  attr_accessible :title, :content, :total_votes

  belongs_to :user

  has_many :votes, :as => :votable, :dependent => :destroy 
end

vote.rb

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

  before_create :update_total

  protected

  def update_total
    self.votable.total_votes ||= 0
    self.votable.total_votes += self.polarity
  end
end

As you can see in vote.rb I want to accomplish the following:

Each time an instance of Vote is created, I want to update the total_votes column of the votable model instance (in this case an instance of Post).

But nothing happens, when I create a vote for a post with post.votes.create(:polarity => 1), the total_votes column of the post still being nil.

Any suggestions to fix this?

EDIT:

This didn’t work either:

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

  before_create :update_total

  protected

  def update_total
    self.votable.total_votes ||= 0
    self.votable.total_votes += self.polarity
    self.votable.save!
  end
end

schema.rb:

create_table "posts", :force => true do |t|
    t.string   "content"
    t.integer  "user_id"
    t.datetime "created_at"
    t.datetime "updated_at"
    t.string   "title"
    t.integer  "comments_count", :default => 0, :null => false
    t.integer  "total_votes"
  end

Answer 1

When you create the Vote object, the Post object already exists. You update it, but you don’t save it. Try with the following code:

def update_total
  self.votable.total_votes ||= 0
  self.votable.total_votes += self.polarity
  self.votable.save!
end