Rails使用has_many through relationship查找和计算

Question

我有以下型号：

产品：

class Product < ActiveRecord::Base
  has_many :product_recommendations, :dependent => :destroy
  has_many :recommendations, :through => :product_recommendations  
end

产品推荐：

class ProductRecommendation < ActiveRecord::Base
  belongs_to :recommendation
  belongs_to :product
end

建议：

class Recommendation < ActiveRecord::Base
  has_many :product_recommendations, :dependent => :destroy
  has_many :products, :through => :product_recommendations
  has_many :recommendation_ratings, :dependent => :destroy
  has_many :ratings, :through => :recommendation_ratings
end

评级：

class Rating < ActiveRecord::Base
  has_many :recommendation_ratings, :dependent => :destroy
  has_many :recommendations, :through => :recommendation_ratings
end

推荐评级：

class RecommendationRating < ActiveRecord::Base
  belongs_to :recommendation
  belongs_to :rating  
end

我如何计算给定推荐的平均评分？我的评级表只包含4条记录（评级1-4），我的推荐控制器中有一个操作，它会更新推荐评级联接表，将评级与推荐关联起来。谢谢

Answer 1

您尝试过吗：

class Product < ActiveRecord::Base
  has_many :product_recommendations, :dependent => :destroy
  has_many :recommendations, :through => :product_recommendations
  has_many :ratings, :through => :recommendations
end

然后

p = Product.find 1
p.ratings.average(:rating)  

这是假设Ratings模型有一个名为rating的int/foat，它存储评级