回调更改的 ActiveRecord 属性? [英] Callback for changed ActiveRecord attributes?

问题描述

我知道 ActiveRecord::Dirty 和相关方法，但我没有看到可以订阅属性更改事件的方法.比如:

I am aware of ActiveRecord::Dirty and the related methods, but I don't see a means by which I can subscribe to an attribute changed event. Something like:

class Person < ActiveRecord::Base
  def attribute_changed(attribute_name, old_value, new_value)
  end

  #or

  attribute_changed do |attribute_name, old_value, new_value|
  end
end

有这方面的 Rails 标准或插件吗?我觉得它一定在某个地方，我只是想念它.

Is there a Rails standard or plugin for this? I feel that it must be there somewhere and I'm just missing it.

推荐答案

cwninja 的答案应该可以解决问题，但还有更多.

cwninja's answer should do the trick, but there is a little bit more to it.

首先，基本属性处理是使用 write_attribute 方法完成的，因此您应该利用它.

First of all, the base attribute handling is done with the write_attribute method so you should be tapping into this.

Rails 也确实有一个内置的回调结构，虽然它不允许传递参数，这有点令人烦恼.

Rails also does have a built in callback structure which could be nice to tap into though it doesn't allow for passing arguments which is a bit of an annoyance.

使用自定义回调你可以这样做:

Using custom callbacks you could do it like this:

class Person < ActiveRecord::Base

  def write_attribute(attr_name, value)
    attribute_changed(attr_name, read_attribute(attr_name), value)
    super
  end

  private

    def attribute_changed(attr, old_val, new_val)
      logger.info "Attribute Changed: #{attr} from #{old_val} to #{new_val}"
    end

 end

如果您想尝试使用 Rails 回调(如果您可能有多个回调和/或子类化特别有用)，您可以执行以下操作:

If you wanted to try to use Rails callbacks (especially useful if you might have multiple callbacks and/or subclassing) you could do something like this:

class Person < ActiveRecord::Base
  define_callbacks :attribute_changed

  attribute_changed :notify_of_attribute_change

  def write_attribute(attr_name, value)
    returning(super) do
      @last_changed_attr = attr_name
      run_callbacks(:attribute_changed)
    end
  end

  private

    def notify_of_attribute_change
      attr = @last_changed_attr
      old_val, new_val = send("#{attr}_change")
      logger.info "Attribute Changed: #{attr} from #{old_val} to #{new_val}"
    end

end

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