scopes_example.rb

# BETTER: move filter logic into Movie class using composable scopes
class Movie < ActiveRecord::Base
  scope :with_good_reviews, lambda { |threshold|
    Movie.joins(:reviews).group(:movie_id).
      having(['AVG(reviews.potatoes) > ?', threshold])
  }
  scope :for_kids, lambda {
    Movie.where('rating in ?', %w(G PG))
  }
end
# in the controller, a single method can now dispatch:
class MoviesController < ApplicationController
  def movies_with_filters
    @movies = Movie.with_good_reviews(params[:threshold])
    @movies = @movies.for_kids          if params[:for_kids]
    @movies = @movies.with_many_fans    if params[:with_many_fans]
    @movies = @movies.recently_reviewed if params[:recently_reviewed]
  end
  # or even DRYer:
  def movies_with_filters_2
    @movies = Movie.with_good_reviews(params[:threshold])
    %w(for_kids with_many_fans recently_reviewed).each do |filter|
      @movies = @movies.send(filter) if params[filter]
    end
  end
end
# in the view:
- @movies.each do |movie|
  -# ...code to display the movie here...