仅当 Rails 中的属性发生更改时才运行回调 [英] Run a callback only if an attribute has changed in Rails

问题描述

我的应用中有以下关联:

I have the following association in my app:

# Page 
belongs_to :status

我想在 page 的 status_id 发生变化时运行回调.

I want to run a callback anytime the status_id of a page has changed.

因此，如果 page.status_id 从 4 变为 5，我希望能够捕捉到它.

So, if page.status_id goes from 4 to 5, I want to be able to catch that.

怎么做?

推荐答案

Rails 5.1+

class Page < ActiveRecord::Base
  before_save :do_something, if: :will_save_change_to_status_id?

  private

  def do_something
    # ...
  end
end

改变 ActiveRecord::Dirty 的提交在这里:https://github.com/rails/rails/commit/16ae3db5a5c6a08383b974ae6c96faac5b4a3c81

The commit that changed ActiveRecord::Dirty is here: https://github.com/rails/rails/commit/16ae3db5a5c6a08383b974ae6c96faac5b4a3c81

这是一篇关于这些变化的博客文章:https://www.fastruby.io/blog/rails/upgrades/active-record-5-1-api-changes

Here is a blog post on these changes: https://www.fastruby.io/blog/rails/upgrades/active-record-5-1-api-changes

以下是我为自己对 Rails 5.1+ 中 ActiveRecord::Dirty 的更改所做的总结:

Here is the summary I made for myself on the changes to ActiveRecord::Dirty in Rails 5.1+:

https://api.rubyonrails.org/classes/ActiveRecord/AttributeMethods/脏.html

修改对象后，保存到数据库之前，或在before_save过滤器内:

After modifying an object and before saving to the database, or within the before_save filter:

• changes 现在应该是 changes_to_save
• changed? 现在应该是 has_changes_to_save?
• changed 现在应该是 changed_attribute_names_to_save
• _change 现在应该是 _change_to_be_saved
• _changed? 现在应该是 will_save_change_to_?
• _was 现在应该是 _in_database

• changes should now be changes_to_save
• changed? should now be has_changes_to_save?
• changed should now be changed_attribute_names_to_save
• <attribute>_change should now be <attribute>_change_to_be_saved
• <attribute>_changed? should now be will_save_change_to_<attribute>?
• <attribute>_was should now be <attribute>_in_database

修改对象并保存到数据库后，或在after_save过滤器内:

After modifying an object and after saving to the database, or within the after_save filter:

• saved_changes(替换previous_changes)
• saved_changes?
• saved_change_to_<属性>
• saved_change_to_<属性>?
• _before_last_save

class Page < ActiveRecord::Base
  before_save :do_something, if: :status_id_changed?

  private

  def do_something
    # ...
  end
end

这利用了 before_save 回调可以根据方法调用的返回值有条件地执行的事实.status_id_changed? 方法来自 ActiveModel::Dirty，它允许我们通过简单地将 _changed? 附加到属性名称来检查特定属性是否已更改.

This utilizes the fact that the before_save callback can conditionally execute based on the return value of a method call. The status_id_changed? method comes from ActiveModel::Dirty, which allows us to check if a specific attribute has changed by simply appending _changed? to the attribute name.

何时应该调用 do_something 方法取决于您的需要.它可以是 before_save 或 after_save 或任何 定义的 ActiveRecord::Callbacks.

When the do_something method should be called is up to your needs. It could be before_save or after_save or any of the defined ActiveRecord::Callbacks.

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