Question

Rails 3.1

I’ll simplify my application to get at my question.

I have two tables: Items and Reviews

Items has a column “Average_Rating” and Reviews has a column “Item_ID” and “Rating”

For each item, I’d like to store the average rating for its corresponding reviews. Although I can’t figure it out, I feel like what I want to do is add something to the create and update methods in the Reviews Controller along the lines of:

@review = Review.find(params[:id])
@item = Item.find(@review.Item_ID)

reviews_to_sum = Reviews.find_by_item_id(@item.id)
@item.Average_Rating = reviews_to_sum.Rating.sum/reviews_to_sum.count

I recognize, however, that the above probably isn’t close to correct… I’m a beginner and I’m stuck.

And I do want to store the Average_Rating in the database, as opposed to calculating it when I need it, for a variety of reasons.

Answer 1

class Item < ActiveRecord::Base
  has_many :reviews
end

class Review < ActiveRecord::Base
  belongs_to :item

  after_save do
    item.update_attributes average_rating: item.reviews.average(:rating)
  end
end