Update Post attribute when new Rating is created

Question

I have a Post model which has many ratings and I would like to store the average ratings figure for each post in the post ratings db column. I have a counter cache on the post model which counts the number of ratings.

I have the following code in my post.rb

def update_rating
    if self.ratings_count_changed? 
      self.rating = self.ratings.average(:rating)
    end
  end

I had this as a before_save callback so whenever the post is edited and saved it updates the ratings, not very useful.

Is there a way I can call this method whenever a new rating is created?

Answer 1

One way of getting closer to your goal is to add after_create callback to Rating model:

class Rating < ActiveRecord::Base
  belongs_to :post

  # ...

  after_create :update_post_average_rating
  def update_post_average_rating
    self.post.update_attributes(:rating => self.post.ratings.average(:rating))
  end
end

Or even more OO friendly version:

class Post < ActiveRecord::Base
  has_many :ratings

  # ...

  def update_average_rating
    update_attributes(:rating => self.ratings.average(:rating))
  end
end

class Rating < ActiveRecord::Base
  belongs_to :post

  # ...

  after_create :update_post_average_rating
  def update_post_average_rating
    self.post.update_average_rating
  end
end