状态机/状态机-转移中的下一个状态。

Question

我正在使用 https://github.com/state-machines/state_machines 来存储对象状态变化前后的工作。我希望有一个单一的方法可在给定集合的“事件”之前被调用，并且对于给定的“事件”，由“before_transition”调用的方法会略有不同。

例如，假设该方法称为 "log_state_change"，则可实现如下功能：

def log_state_change
  case <???>
  when "successful"
    Rails.logger.info "Successful"
  when "failure"
    Rails.logger.info "Failure"
  when "starting_run"
    Rails.logger.info "Starting run" 
  else
    Rails.logger.error "Unknown"
end

我找不到适合上面的<???>标签的方法。也许熟悉这个技术的人能够提供帮助？

- CDub

---

你的意思是所有这些都应该像'successful'或:successful这样作为值而不是变量吗？我猜测case state可以完成任务，它会返回一个字符串。永远不要低估Rails.logger.info(state.titleize)这样的东西。 - tadman

我确实在转换状态，但是我正在转变为的状态，而不是我当前所处的状态。我会更新问题以反映这个状态字符串。 - CDub

Answer 1

你可以在你的 before_transition 回调函数中接受一个参数，并获取实施预期行为所需的所有数据。传递参数的代码可以在 库的源代码 中找到。你也可以使用 around_transition 实现此逻辑。

require 'state_machines'

class Light

  state_machine :state, initial: :off do

    before_transition from: any, do: :log_me

    event :light do
      transition all => :on
    end

    event :dark do
      transition [:on] => :off
    end

  end

  def log_me(transition)
    case transition.event
    when :light
      p "`light` event was called to transition from #{transition.from} to #{transition.to}"
    when :dark
      p "`dark` event was called to transition from #{transition.from} to #{transition.to}"
    else
      p "`#{transition.event}` was called to transition from #{transition.from} to #{transition.to}"
    end
  end
end

a = Light.new

a.light # => "`light` event was called to transition from off to on"
a.dark # => "`dark` event was called to transition from on to off"

- achempion