Rails Query 通过直通类将子类与父类结合起来

Question

我有以下课程

class Order
   has_many :order_issues, through: :order_deliveries, inverse_of: :order
end

class OrderDelivery
   has_many :order_issues, as: :issuable, inverse_of: :order_delivery
   belongs_to :order, inverse_of: :order_deliveries
end

class OrderIssue
   belongs_to :order, inverse_of: :order_issues
   belongs_to :order_delivery, inverse_of: :order_issues
end

当我尝试时

Order.joins(:order_issues).to_sql 


SELECT orders.* 
FROM orders 
INNER JOIN order_deliveries 
   ON order_deliveries.order_id = orders.id 
INNER JOIN order_issues 
   ON order_issues.issuable_id = order_deliveries.id 
      AND order_issues.issuable_type = 'OrderDelivery' 

它按预期工作。但是，当我尝试

OrderIssue.joins(:order).to_sql

SELECT order_issues.id 
FROM order_issues 
INNER JOIN orders 
    ON orders.id = order_issues.order_id

为什么不一样？理想情况下，我希望 SQL 查询如下所示，以提供OrderIssue 活动记录

SELECT order_issues.* 
FROM order_issues 
INNER JOIN order_deliveries ON order_issues.issuable_id = order_deliveries.id 
       AND order_issues.issuable_type = 'OrderDelivery'
INNER JOIN orders 
    ON order_deliveries.order_id = orders.id 

Answer 1

inverse_of仅用于避免重复检索相同记录；它不会改变 ActiveRecord 关系解析的行为。

在这种情况下，设置 has_many :order_issues 而不使用 :through 选项似乎是正确的用法，并且会得到您正在寻找的查询，因为 OrderIssue 直接 belongs_to :order。 OrderDelivery 也应相应更新。

class Order
  has_many :order_issues
  has_many :order_deliveries
end

class OrderDelivery
  belongs_to :order
  has_many :order_issues, through: :order
end

class OrderIssue
  belongs_to :order
  has_many :order_deliveries, through: :order
end