如何在 Rails/ActiveRecord 中锁定父记录？

Question

当有一个父记录关联多个子记录时，对父记录使用行锁定是确保一致性的明显方法。但是，我似乎找不到在 ActiveRecord 中执行此操作的干净方法。

---

例如，假设我们有两个模型：Order 和 OrderProduct。

class Order < ActiveRecord::Base
  has_many :order_products
  ...
end

class OrderProduct < ActiveRecord::Base
  belongs_to :order
  ...
end

更新OrderProduct 会影响Order 的整体状态，因此我们要确保在任何给定时间只有一个事务在更新Order。

如果我们在编辑 OrderProduct 时尝试实现这一点，我能看到的 ruby​​ 中最简洁的方法是：

def edit
  product = OrderProduct.find params[:id]
  Order.transaction do
    product.order.lock!
    # Make sure no changes have occurred while we were waiting for the lock
    product.reload

    # Do stuff...
    product.order.some_method
  end
end

但是，如果 SQL 查询效率很低，则会产生：

SELECT "order_products".* FROM "order_products" WHERE "order_products"."id" = $1 LIMIT 1 [["id", "2"]]
SELECT "orders".* FROM "orders" WHERE "orders"."id" = 2 LIMIT 1
SELECT "orders".* FROM "orders" WHERE "orders"."id" = $1 LIMIT 1 FOR UPDATE  [["id", 2]]
SELECT "order_products".* FROM "order_products" WHERE "order_products"."id" = $1 LIMIT 1 [["id", 2]]
SELECT "orders".* FROM "orders" WHERE "orders"."id" = 2 LIMIT 1

---

我们可以通过将 更改为以下内容来减少查询次数：

def edit
  product = OrderProduct.find params[:id]
  Order.transaction do
    order = Order.find product.order_id, lock: true
    # Make sure no changes have occurred while we were waiting for the lock
    product.reload
    # Cache the association
    product.order = order

    # Do stuff...
    product.order.some_method
  end
end

产生更好的 SQL：

SELECT "order_products".* FROM "order_products" WHERE "order_products"."id" = $1 LIMIT 1 [["id", "2"]]
SELECT "orders".* FROM "orders" WHERE "orders"."id" = 2 LIMIT 1 FOR UPDATE  [["id", 2]]
SELECT "order_products".* FROM "order_products" WHERE "order_products"."id" = $1 LIMIT 1 [["id", 2]]

但是代码比较混乱。

有没有更简洁的方法来使用 ActiveRecord？ 调用 product.order = order 只是为了缓存关联似乎有点危险。

Answer 1

有关简单的 Rails 锁定方式，请查看http://api.rubyonrails.org/classes/ActiveRecord/Locking/Pessimistic.html

Answer 2

.lock.load

是您正在寻找的。 大概？