使用pluginaweek的state_machine，我可以在事件期间引用activerecord对象吗？

Question

我正在尝试实现一个“挂起”事件，将对象转换为：挂起状态。但我需要能够“取消暂停”，并返回到之前的状态。我向模型添加了 previous_state 字段，但我看不到如何在事件块内访问它。

这是我试图实现的基本逻辑：

event :suspend do
  owner.previous_state = self.state
  transition [:new, :old] => :suspended
end

event :unsuspend do
  transition :suspended => owner.previous_state.to_sym
  owner.previous_state = nil
end

state_machine 文档并不是很有帮助，而且我在网上找不到示例。有时很难知道如何向谷歌描述某些东西:)

Answer 1

state_machine 的作者还在这里提供了替代解决方案：https://groups .google.com/d/msg/pluginaweek-talk/LL9VJdL_x9c/vP1qv6br734J

也就是说：

另一个可能的解决方案是对状态机的工作方式进行一些创意。 ActiveRecord 等 ORM 中有很多钩子，使我们能够在流程的任何阶段设置状态。请考虑以下情况：

class Vehicle < ActiveRecord::Base
  before_validation do |vehicle|
    # Set the actual value based on the previous state if we've just restored
    vehicle.state = vehicle.previous_state if vehicle.restored?
  end

  state_machine :initial => :parked do
    event :ignite do
      transition :parked => :idling
    end

    event :restore do
      transition any => :restored
    end

    state :parked do
      validates_presence_of :name
    end
  end

  # Look up previous state here...
  def previous_state
    'parked'
  end
end

在此示例中，引入了一个新状态（已恢复），即使它从未真正保留在数据库中。相反，我们提供了一个 before_validation 钩子，它根据先前的状态重写状态。您可以看到下面的结果：

v = Vehicle.new(:name => 'test')  # => #<Vehicle id: nil, name: "test", state: "parked">
v.save                            # => true
v.name = nil                      # => nil
v.ignite                          # => true
v                                 # => #<Vehicle id: 1, name: nil, state: "idling">
v.restore                         # => false
v.errors                          # => #<OrderedHash {:name=>["can't be blank"]}>
v.state                           # => "idling"
v.name = 'test'                   # => "test"
v.restore                         # => true
v                                 # => #<Vehicle id: 1, name: "test", state: "parked">
v.parked?                         # => true

这应该需要减少一次数据库命中，因为它发生在验证之前。就我而言，完整的图片如下所示：

module Interpreting::Status

  extend ActiveSupport::Concern

  included do

    before_validation :restore_previous_state, if: :interpreter_cancelled?

    state_machine :state, :initial => :ordered do

      before_transition :to => :interpreter_booked, :do => :set_previous_state

      state :ordered

      state :confirmed

      state :interpreter_booked

      state :interpreter_cancelled # Transient status
    end

  end


protected

  def set_previous_state
    self.previous_state = self.state
  end

  def restore_previous_state
    self.state = self.previous_state
  end

end

Answer 2

在我看来，这不是一个完美的解决方案，但我确实弄清楚了如何完成我的任务：

state_machine :initial => :new do
  state :new

  state :old

  state :suspended
  before_transition :to => :suspended, :do => :set_previous_state

  state :unsuspended
  after_transition :to => :unsuspended, :do => :restore_previous_state

  event :suspend do
    transition any - :suspended => :suspended
  end

  event :unsuspend do
    transition :suspended => :unsuspended, :if => :previous_state_present?
  end
end

private

def previous_state_present?
  previous_state.present?
end

def set_previous_state
  self.previous_state = state
end

def restore_previous_state
  if previous_state
    self.state = previous_state
    self.previous_state = nil
  end
end

我首先向我的机器添加“未挂起”状态。虽然我从不想让某些东西保持在这种状态，但我无法动态地告诉 state_machine 我想要取消挂起到什么状态。

我向挂起事件添加了 before_transition 回调，以保存挂起之前的状态。

我向取消挂起事件添加了 after_transition 回调，因此状态会立即更新到之前的状态，然后擦除之前的状态以防止在对象生命周期的后期出现问题。

这并不完美。它可以工作，但它比仅仅将挂起和取消挂起事件创建为独立方法要复杂得多。我没有走这条路，因为我希望 state_machine 控制所有状态更改，并且突破该路线会消除防止移至/移出无效状态、回调等的保护。

Answer 3

简单的解决方案

我提供了使用 owner 块参数的解决方案的替代版本。在某些情况下可能有用。

state_machine :initial => :new do
  state :new
  state :old

  before_transition :on => :suspend do |owner|
    owner.previous_state = owner.state
  end

  before_transition :on => :unsuspend do |owner|
    owner.previous_state.present?
  end

  after_transition :on => :unsuspend do |owner|
    owner.state = owner.previous_state
  end

  event :suspend do
    transition any - :suspended => :suspended
  end

  event :unsuspend do
    transition :suspended => :unsuspended
  end
end

around_transition 的使用

另请注意，您可以用 around_transition 替换两个 unsuspend 块：

around_transition :on => :unsuspend do |owner, transition_block|
  if owner.previous_state.present?
    transition_block.call
    owner.state = owner.previous_state
  end
end