Question

I have a Rails 3 application I’m working on. I have 3 models: User, Venue, and Rating.

User.rb:

# attributes:
# name, email => String
class User < ActiveRecord::Base
    has_many :ratings
    has_many :venues, :through => :ratings, :uniq => true
    ...
end

Venue.rb:

# attributes: 
# name, address, city, state, zip, neighborhood => String
# latitude, longitude => Float
class Venue < ActiveRecord::Base
    has_many :ratings
    has_many :users
    ...

    def average_rating
      sum = 0
      self.ratings.each do |rating|
         sum += rating.value
      end
      sum.to_f / self.number_of_ratings.to_f
    end

    def number_of_ratings
      self.ratings.count
    end
end

Rating.rb:

# attributes: 
# venue_id, user_id => Integer
# value => String
class Rating < ActiveRecord::Base
    belongs_to :user
    belongs_to :venue
    ...
end

I need to get all venues grouped by neighborhood, with the name of the neighborhood, the average rating for all venues in the neighborhood group, the total number of ratings for all venues in the neighborhood group, the average latitude of all venues in the neighborhood group, and the average longitude of all venues in the neighborhood group.

I’m not quite sure how to get there using ActiveRecord and Postgres, any suggestions?

Answer 1

This is what I’ve done to make it work; however, I feel like their might be a more efficient way to run a postres query and group by neighborhood, but I haven’t had any luck in figuring it out.

neighborhoods = @venues.select('DISTINCT(venues.neighborhood)').map(&:neighborhood)
neighborhoods.each do |neighborhood|
    venues_in_neighborhood = @venues.where(:neighborhood => neighborhood).includes(:ratings)
    avg_rating = venues_in_neighborhood.average('ratings.value').to_f        
    number_of_ratings = Rating.includes(:venue).where('venues.neighborhood' => neighborhood).count
    avg_latitude = venues_in_neighborhood.average('latitude').to_f
    avg_longitude = venues_in_neighborhood.average('longitude').to_f

    @response << {:name => neighborhood, 
                  :latitude => avg_latitude, 
                  :longitude => avg_longitude, 
                  :rating => avg_rating,
                  :numberOfRatings => number_of_ratings}
end