ruby-on-rails - :highest_rated scope to order by average rating

Question

我有一个Product，每个产品都有_many ratings。我正在尝试创建一个 :highest_rated Product 范围，它按产品的最高平均评级对产品进行排序(每个评级都在 ratings 表中)。我试过这个:

scope :highest_rated, includes(:ratings).order('avg(ratings.rating) DESC')

但这给了我一个 misuse of aggregate: avg() 错误。

关于如何按最高平均评分订购我的产品的任何提示？

Answer 1

这个有效:

scope :highest_rated, includes(:ratings).group('product_id').order('AVG(ratings.rating) DESC')

仅获取具有现有评级的产品:

scope :highest_rated, includes(:ratings).group('product_id').where('ratings.rating IS NOT NULL').order('AVG(ratings.rating) DESC')

编辑:以上内容在 PostgreSQL 中不起作用。我改用它(它在 SQLite 和 PostgreSQL 中都有效):

scope :highest_rated, where("products.id in (select product_id from ratings)").group('products.id, products.name, products.all_other_fields').joins(:ratings).order('AVG(ratings.rating) DESC')