ruby-on-rails – 当将child设置为“nil”时,Rails / ActiveReco

假设我们有这个设置：

class User < ApplicationRecord
  has_one :subscription
end

class Subscription < ApplicationRecord
  belongs_to :user
end

没有“依赖：毁灭”

> user = User.create(name: "Bob")
> user.subscription = Subscription.create(provider: "Stripe")

> user.subscription = nil

   (0.1ms)  begin transaction
  SQL (0.4ms)  UPDATE "subscriptions" SET "user_id" = ?,"updated_at" = ? WHERE "subscriptions"."id" = ?  [["user_id",nil],["updated_at",2017-01-10 19:24:56 UTC],["id",2]]
   (2.0ms)  commit transaction

随着“依赖：毁灭”

class User < ApplicationRecord
  has_one :subscription,dependent: :destroy
end


> user = User.create(name: "Bob")
> user.subscription = Subscription.create(provider: "Stripe")

> user.subscription = nil

   (0.1ms)  begin transaction
    SQL (1.1ms)  DELETE FROM "subscriptions" WHERE "subscriptions"."id" = ?  [["id",1]]
   (0.7ms)  commit transaction

这是预期的行为吗？我真的很惊讶,根本没有显式调用save或destroy或update等进行SQL调用.我也很困惑为什么依赖：destroy在这种情况下改变行为.

这应该发生,如果是这样,它是否记录在任何地方？依赖：破坏版本似乎特别危险.

这是使用Rails 5以及Rails 4的几个版本测试的.