Ruby-on-rails 仅当 Rails 中的属性发生更改时才运行回调

Run a callback only if an attribute has changed in Rails

提问by Hommer Smith

I have the following association in my app:

我的应用程序中有以下关联：

# Page 
belongs_to :status

I want to run a callback anytime the status_idof a pagehas changed.

我想在status_idapage发生变化时运行回调。

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

所以，如果page.status_id从 4 到 5，我希望能够抓住它。

How to do so?

怎么做？

回答by pdobb

Rails 5.1+

导轨 5.1+

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

  private

  def do_something
    # ...
  end
end

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

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

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

这是有关这些更改的博客文章：https: //www.ombulas.com/blog/rails/upgrades/active-record-5-1-api-changes.html

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

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

ActiveRecord::Dirty

ActiveRecord::Dirty

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

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

Before Saving (OPTIONAL CHANGE)

保存前（可选更改）

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

在修改对象之后和保存到数据库之前，或在before_save过滤器中：

• changesshould now be changes_to_save
• changed?should now be has_changes_to_save?
• changedshould now be changed_attribute_names_to_save
• <attribute>_changeshould now be <attribute>_change_to_be_saved
• <attribute>_changed?should now be will_save_change_to_<attribute>?
• <attribute>_wasshould now be <attribute>_in_database

• 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
• <attribute>_change现在应该是 <attribute>_change_to_be_saved
• <attribute>_changed?现在应该是 will_save_change_to_<attribute>?
• <attribute>_was现在应该是 <attribute>_in_database

After Saving (BREAKING CHANGE)

保存后（中断更改）

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

修改对象并保存到数据库后，或在after_save过滤器内：

• saved_changes(replaces previous_changes)
• saved_changes?
• saved_change_to_<attribute>
• saved_change_to_<attribute>?
• <attribute>_before_last_save

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

---

---

Rails <= 5.0

导轨 <= 5.0

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

  private

  def do_something
    # ...
  end
end

This utilizes the fact that the before_savecallback 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.

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。该status_id_changed?方法来自ActiveModel::Dirty，它允许我们通过简单地附加_changed?到属性名称来检查特定属性是否已更改。

When the do_somethingmethod should be called is up to your needs. It could be before_saveor after_saveor any of the defined ActiveRecord::Callbacks.

何时do_something调用该方法取决于您的需要。它可以是before_save或after_save或任何已定义的 ActiveRecord::Callbacks。

回答by Mateus Luiz

The attribute_changed?is deprecated in Rails 5.1, now just use will_save_change_to_attribute?.

在attribute_changed?被弃用的Rails 5.1，现在只需使用will_save_change_to_attribute?。

For more information, see this issue.

有关更多信息，请参阅此问题。

回答by Monideep

Try this

尝试这个

after_validation :do_something, if: ->(obj){ obj.status_id.present? and obj.status_id_changed? } 

def do_something
 # your code
end

Reference - http://apidock.com/rails/ActiveRecord/Dirty

参考 - http://apidock.com/rails/ActiveRecord/Dirty