Rails 选择最受欢迎的产品

Question

我需要获取“10 种最受欢迎​​”产品的列表。我认为最好的方法是使用引用Products 的Orders 表（模型）。

我知道我应该做什么，但我不知道怎么写。这就是我在 MySQL 中的做法：

SELECT  products.* 
FROM (SELECT product_id, count(product_id) as count from Orders 
           GROUP BY product_id
           ORDER BY count DESC
           LIMIT 10) AS O
LEFT OUTER JOIN products
ON Products.id  = O.product_id

如何在 Rails 中编写查询？

例如： Order.group(:product_id).count...

Answer 1

试试

# One single query with join (extract the subquery and 
# assign it to an alias t using active_record function .from)
Product.joins("INNER JOIN t ON t.product_id = products.id")
       .from(
         Order
            .select("orders.product_id, COUNT(orders.id) as count")
            .group("orders.product_id").order("count DESC").limit(10), 
       :t)

# Alternative, but I think it will use 2 queries, 
# and the first one is probably faster
Product
      .where(id: 
      Order
         .select("orders.product_id, COUNT(orders.id) as count")
         .group("orders.product_id").order("count DESC").limit(10).pluck(:product_id))

更新：

该代码对我有用 (@KazKazar)：

Product.joins("INNER JOIN products ON products.id = O.product_id") .from(Order.select("product_id, COUNT(product_id) as count") .group("product_id").order("count DESC").limit(10),:O)