ruby-on-rails - around_action 回调如何工作？需要解释

Question

我对 around_action 感到非常困惑。它们是如何工作的？有人可以向我提供他们如何工作的示例/解释吗？

这是我的敏捷 Web 开发 4 书中的引述:

Around callbacks wrap the execution of actions. You can write an around callback in two different styles. In the first, the callback is a single chunk of code. That code is called before the action is executed. If the callback code invokes yield, the action is executed. When the action completes, the callback code continues executing. Thus, the code before the yield is like a before action callback and the code after the yield is the after action callback. If the callback code never invokes yield. the action is not run-this is the same as having a before action callback return false.

当我读到这里时，我有点明白了。这是 Rails 指南中的示例

class ChangesController < ApplicationController
  around_action :wrap_in_transaction, only: :show

  private

  def wrap_in_transaction
    ActiveRecord::Base.transaction do
      begin
        yield
      ensure
        raise ActiveRecord::Rollback
      end
    end
  end
end

那么这里发生了什么？ ActiveRecord::Base.transaction 是否以“之前”部分开始，并将 ActiveRecord::Rollback 提升为“之后”部分？这种方法屈服于什么？是节目吗？最后是什么会导致 yield 方法失​​败导致整个回调失败？会是表演 Action 的渲染吗？我不明白。请帮忙。

Answer 1

我的理解如下:

begin
    # Do before action...
    logger.info 'I am the before action'

    # Do the action, which is passed as a block to your "around filter"
    # Note that if you were to delete this line, the action will never be called!
    yield

    # Do after action...
    logger.info 'I am the after action'
ensure
    raise ActiveRecord::Rollback
end