ruby-on-rails - 以编程方式定义 around_ 回调时为 "no block given"

Question

我正在尝试编写一个库，以编程方式将 around_update/around_destroy 回调添加到 ActiveRecord 模型。

因此，常规模型看起来像这样并且按预期工作:

class User < ActiveRecord::Base
  around_update :test_update

  def test_update
    Rails.logger.debug "test_update"
    yield
    Rails.logger.debug "Finished test_update"
  end
end

u=User.last
u.name = 'something'
u.save

######### output (as expected):
# test_update
# Finished test_update

我的小图书馆(显然只是骨架)看起来像这样:

# A module for creating around callbacks in a model
module Piddle
  module TimelineFor
    def self.included(klass)
      klass.send(:extend, ClassMethods)
    end

    module ClassMethods
      def timeline_for(event, opts={})
        method_name = :"timeline_for_#{event.to_s}"
        define_method(method_name) do |&block|
          Rails.logger.debug method_name.to_s
          yield block
          Rails.logger.debug "After yield in #{method_name.to_s}"
        end

        send(:around_update, method_name)
      end
    end
  end
end

它定义了一个 timeline_for 方法，该方法应该添加 timeline_for_update 方法并使其成为 around_update 事件的回调。我想使用的用户模型是这样的:

# second version of the User model using Piddle to create the callback
require 'piddle/piddle'

class User < ActiveRecord::Base
  include Piddle::TimelineFor

  timeline_for :update
end

u=User.last
u.name = 'gfgfhfhfgh'
u.save

在我看到的输出中

timeline_for_update
LocalJumpError: no block given (yield)
from /vagrant/lib/piddle/piddle.rb:13:in `block in timeline_for'

第一行输出表示正在调用方法但未传入 block 。

任何想法或替代实现？

Answer 1

问题是，如果您从 define_method 调用 yield，ruby 会将其解释为试图屈服于传递给 timeline_for 的(不存在的) block ，不是 block rails 传递给 timeline_for_foo

您已将 block 传递给您，因此您可以直接调用它:

def timeline_for event
  method_name = "timeline_for_#{event}"
  define_method method_name do |&block|
    ActiveRecord::Base.logger.debug "before #{method_name} yield" 
    block.call
    ActiveRecord::Base.logger.debug "after #{method_name} yield" 
  end
  send :around_update, method_name.to_sym #must use a symbol here
end