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

问题描述

我的应用程序具有以下关联：

 ＃页面
属于：状态
  

我想在 status_id 中的任何时候运行回调c $ c>页面已更改。

因此，如果 page.status_id 从4变为5，我希望能够抓住它。 / p>

该怎么做？

解决方案

Rails 5.1 +

  class Page< ActiveRecord :: Base 
 before_save：do_something，如果：：will_save_change_to_status_id？ 
 
私人
 
 def do_something 
＃... 
结束
结束
  

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

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

这是我为自己做的关于ActiveRecord更改的摘要： ：Dirty in Rails 5.1 +：

ActiveRecord :: Dirty

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

保存前（OPTIO NAL更改）

在修改对象之后并保存到数据库之前，或者在 before_save 过滤器内：

• 更改现在应为 changes_to_save


• 已更改？现在应为 has_changes_to_save？


• 已更改现在应为 changed_attribute_names_to_save


• < attribute__change 现在应为< attribute__change_to_be_saved


• < attribute_gt__changed？现在应该是 will_save_change_to_< attribute>？


• < attribute__was 现在应该是< attribute__in_database

保存后（BREAKING CHANGE）

修改对象并保存到数据库后，或在<$ c $之内c> after_save 过滤器：

• 保存的更改（重复ace 上一个更改）


• 保存的更改？


• saved_change_to_< attribute>


• saved_change_to_to_< attribute？ / li>

• < attribute__before_last_save



---

Rails< = 5.0

  class Page< ActiveRecord :: Base 
 before_save：do_something，如果：：status_id_changed？ 
 
私人
 
 def do_something 
＃... 
结束
结束
  

这利用了以下事实： before_save 回调可以根据方法调用的返回值有条件地执行。 status_id_changed？方法来自 ActiveModel： ：Dirty ，它使我们可以通过在属性名称后附加 _changed？来检查特定属性是否已更改。

何时应调用 do_something 方法取决于您的需要。可以是 before_save 或 after_save 或任何定义的ActiveRecord :: Callbacks 。

I have the following association in my app:

# Page 
belongs_to :status

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

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

How to do so?

解决方案

Rails 5.1+

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

  private

  def do_something
    # ...
  end
end

The commit that changed ActiveRecord::Dirty is here: 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

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

ActiveRecord::Dirty

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

Before Saving (OPTIONAL CHANGE)

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

• 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

After Saving (BREAKING CHANGE)

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

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

---

Rails <= 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_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.

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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