Rails计算平均值

Question

我有一个rake任务，我正在计算一组产品的平均值，但是我无法计算和更新每个集合中的个人的属性。我有什么至今：

task :calculate_rating => :environment do 
total_rating = [] 
    Product.find(:all, :joins => :rating_sets, :conditions => ["rating_set_id = ?", 45 ]).each do |product| 
    Rating.find(:all, :conditions => ["rating_set = ? and product_id =?", 45 ,product.id]).each do |ratings| 
    total_rating << ratings.rating 
     end 
     average = total_rating.inject(:+).to_f/total_rating.size 
     q = ProductRatingSet.find_by_product_id_and_rating_set_id(@product_id, 45) 
     q.update_attribute(:product_rating, average) 
     end 
     end 

我试着去寻找基本上平均和更新product_rating每个由Rating.find(:all, :conditions => ["rating_set = ? and product_id =?", 45 ,product.id])检索集。

Answer 1

试图把total_rating阵列的初始化你的第一个循环

Product.find(:all, :joins => :rating_sets, :conditions => ["rating_set_id = ?", 45 ]).each do |product| 
    total_rating = [] 
    Rating.find(:all, :conditions => ["rating_set = ? and product_id =?", 45 ,product.id]).each do |ratings| 
    total_rating << ratings.rating 
    end 
    average = total_rating.inject(:+).to_f/total_rating.size 
    q = ProductRatingSet.find_by_product_id_and_rating_set_id(@product_id, 45) 
    q.update_attribute(:product_rating, average) 
end