Question

I am using Ruby 1.9.2, Rails 3.1. I have the following:

# review.rb
def calculate_rating
  all_rating = Review.select("rating").where("reviewable_id = ?", self.reviewable_id)
  all_rating.inject(:+)
end

# reviews_controller.rb
def create
  @reviewable = find_reviewable
  @review = @reviewable.reviews.where("user_id = ?", current_user).first
  if @review.save
    @review.calculate_rating
    redirect_to :id => nil
  else
    flash[:error] = 'Error saving review. Please try again.'
    redirect_to :id => nil
  end
end

The idea behind this is that when a new review with rating is submitted and saved, it will find all ratings for all @reviewable, sum all the ratings and divide by the total number of ratings.

Problem that I am facing currently is this line: all_rating = Review.select("rating").where("reviewable_id = ?", self.reviewable_id) where all_rating returns an array of objects, like below:

[#<Review rating: #<BigDecimal:1050f0a40,'0.3E1',9(18)>>, #<Review rating: #<BigDecimal:1050f0928,'0.1E1',9(18)>>]

which I can’t do any arithmetic calculation to it. I need it to be an array of numbers before I could use the inject to sum it and divide by the number of ratings.

Please advise me how I can get the inject to work. Many thanks!

Answer 1

AR/SQL (faster):

Review.select("rating").where(:reviewable_id => self.reviewable_id).sum(:rating)

Ruby (slower):

Review.select("rating").where(:reviewable_id => self.reviewable_id).map(&:rating).sum