如何在Rails中获取属性的原始值 [英] How to get the original value of an attribute in Rails

问题描述

有没有办法获取 ActiveRecord 属性的原始值(=从数据库加载的值)?

is there a way to get the original value that an ActiveRecord attribute (=the value that was loaded from the database)?

我想在观察者身上有这样的东西

I want something like this in an observer

before_save object
  do_something_with object.original_name
end

任务是在更新时从哈希表中删除对象(实际上是将其移动到表中的另一个键).

The task is to remove the object from a hash table (in fact, move it to another key in the table) upon updating.

推荐答案

Rails 5.1 之前

将 _was 附加到您的属性将为您提供以前的值.

Before rails 5.1

Appending _was to your attribute will give you the previous value.

从下面 Lucas Andrade 的回答中复制:https://stackoverflow.com/a/50973808/9359123

附加 _was 在 rails 5.1 中被弃用，现在你应该附加 _before_last_save

Appending _was is deprecated in rails 5.1, now you should append _before_last_save

类似于:

before_save object
  do_something_with object.name_before_last_save
end

将返回上次保存在数据库之前的名称值(适用于保存和创建)


根据文档，_was 和 _before_last_save 之间的区别:

Will return the name value before your last save at database (works for save and create)


The difference between _was and _before_last_save according to the documentation:

_was 来源 来自文档

def attribute_was(attr)
  attribute_changed?(attr) ? changed_attributes[attr] : __send__(attr)
end

_before_last_save 来源来自文档

def attribute_before_last_save(attr_name)
  mutations_before_last_save.original_value(attr_name)
end

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