Question

问题：

我需要知道在块内调用的记录属性（比如我需要类似下面的内容）：

def my_custom_method(&block)
  some_method_that_starts_tracking

  block.call

  some_method_that_stops_tracking

  puts some_method_that_returns_called_records_attributes
  do_something_about(some_method_that_returns_called_records_attributes)
end

my_custom_method { somecodethatcallsauthorofbook1andemailandfirstnameofuser43 }

# this is the `puts` output above (just as an example)
# => {
#      #<Book id:1...>  => [:author],
#      #<User id:43...> => [:email, :first_name]
#    }

块内的代码可以是任何
具体来说，我的意思是跟踪ApplicationRecord的子类的任何实例，因此它可以是Book，User等任何模型的实例......

尝试：

根据我的理解，这类似于rspec在预期调用方法时的工作方式。它以某种方式跟踪该方法的任何调用。所以，我最初的尝试是做类似以下的事情（这还没有完全奏效）：

def my_custom_method(&block)
  called_records_attributes = {}

  ApplicationRecord.descendants.each do |klass|
    klass.class_eval do
      attribute_names.each do |attribute_name|
        define_method(attribute_name) do
          called_records_attributes[self] ||= []
          called_records_attributes[self] << attribute_name
          self[attribute_name]
        end
      end
    end
  end

  block.call

  # the above code will work but at this point, I don't know how to clean the methods that were defined above, as the above define_methods should only be temporary

  puts called_records_attributes
end

my_custom_method { Book.find_by(id: 1).title }
# => {
#      #<Book id: 1...> => ['title']
#    }

上面的.descendants可能不是一个好主意，因为如果我没弄错的话，Rails会使用autoload
正如上面在评论中已经说过的那样，我不知道如何删除这些“defined_methods”，它们只是在这个“块”的持续时间内只是暂时的。
此外，我上面的代码可能会覆盖模型的“实际”属性getter，如果已经定义了任何一个，那就不好了。

背景：

我正在编写一个gem live_record，我正在添加一个新功能，允许开发人员只需编写类似

的内容

<!-- app/views/application.html.erb -->
<body>
  <%= live_record_sync { @book.some_custom_method_about_book } %>
</body>

...将在页面上呈现@book.some_custom_method_about_book，但同时live_record_sync包装器方法会记录在该块内调用的所有属性（即在some_custom_method_about_book内调用@book.title，然后将这些属性设置为块自己的“依赖关系”，稍后当该特定书籍的属性更新时，我也可以直接更新HTML该属性是“依赖”的页面，如上所述。我知道这不是一个准确的解决方案，但我想先通过实验来开辟我的机会。

- Rails 5

Answer 1

免责声明：我认为这只是一个平庸的解决方案，但希望可以帮助任何有同样问题的人。

我尝试阅读 rspec 源代码，但因为我无法轻易理解幕后发生的事情，而且我发现 rspec ＆＃39; s（ie）expect(Book.first).to receive(:title)与我真正想要的不同，因为已经指定了方法（即:title），而我想要的是跟踪任何属性的方法，因为在这两个原因中，我跳过了进一步的阅读，并尝试了我自己的解决方案，希望以某种方式工作;见下文。

请注意，我在这里使用Thread local-storage，因此此代码应该是线程安全的（尚未测试）。

# lib/my_tracker.rb
class MyTracker
  Thread.current[:my_tracker_current_tracked_records] = {}

  attr_accessor :tracked_records

  class << self
    def add_to_tracked_records(record, attribute_name)
      Thread.current[:my_tracker_current_tracked_records][{model: record.class.name.to_sym, record_id: record.id}] ||=  []
      Thread.current[:my_tracker_current_tracked_records][{model: record.class.name.to_sym, record_id: record.id}] << attribute_name
    end
  end

  def initialize(block)
    @block = block
  end

  def call_block_while_tracking_records
    start_tracking

    @block_evaluated_value = @block.call
    @tracked_records = Thread.current[:my_tracker_current_tracked_records]

    stop_tracking
  end

  def to_s
    @block_evaluated_value
  end

  # because I am tracking record-attributes, and you might want to track a different object / method, then you'll need to write your own `prepend` extension (look for how to use `prepend` in ruby)
  module ActiveRecordExtensions
    def _read_attribute(attribute_name)
      if Thread.current[:my_tracker_current_tracked_records] && !Thread.current[:my_tracker_is_tracking_locked] && self.class < ApplicationRecord
        # I added this "lock" to prevent infinite loop inside `add_to_tracked_records` as I am calling the record.id there, which is then calling this _read_attribute, and then loops.
        Thread.current[:my_tracker_is_tracking_locked] = true
        ::MyTracker.add_to_tracked_records(self, attribute_name)
        Thread.current[:my_tracker_is_tracking_locked] = false
      end
      super(attribute_name)
    end
  end

  module Helpers
    def track_records(&block)
      my_tracker = MyTracker.new(block)
      my_tracker.call_block_while_tracking_records
      my_tracker
    end
  end

  private

  def start_tracking
    Thread.current[:my_tracker_current_tracked_records] = {}
  end

  def stop_tracking
    Thread.current[:my_tracker_current_tracked_records] = nil
  end
end

ActiveSupport.on_load(:active_record) do
  prepend MyTracker::ActiveRecordExtensions
end

ActiveSupport.on_load(:action_view) do
  include MyTracker::Helpers
end

ActiveSupport.on_load(:action_controller) do
  include MyTracker::Helpers
end

使用示例

<强> some_controller.rb

book = Book.find_by(id: 1)
user = User.find_by(id: 43)

my_tracker = track_records do
  book.title
  if user.created_at == book.created_at
    puts 'same date'
  end
  'thisisthelastlineofthisblockandthereforewillbereturned'
end

puts my_tracker.class
# => #<MyTracker ... >

puts my_tracker.tracked_records
# => {
#      {model: :Book, record_id: 1} => ['title', 'created_at'],
#      {model: :User, record_id: 43} => ['created_at']
#    }

puts my_tracker
# => 'thisisthelastlineofthisblockandthereforewillbereturned'
# notice that `puts my_tracker` above prints out the block itself
# this is because I defined `.to_s` above.
# I need this `.to_s` so I can immediately print the block as-is in the views.
# see example below

<强> some_view.html.erb

<%= track_records { current_user.email } %>

P.S。也许我把它作为一个宝石包装起来会更好。如果您有兴趣，请告诉我

如何跟踪块内“被叫”的对象？

问题：

尝试：

背景：

1 个答案:

使用示例