如何在 Rails 中获取属性的原始值

Before rails 5.1

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

For rails 5.1+

Copied from Lucas Andrade's answer below: https://stackoverflow.com/a/50973808/9359123

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

Something like:

before_save object
do_something_with object.name_before_last_save
end

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 source from docs

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

_before_last_save source from docs

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

ActiveRecord's attributes_before_type_cast method returns a hash of attributes before typecasting and deserialization have occurred.

Take a look in rails documentation

http://api.rubyonrails.org/classes/ActiveModel/Dirty.html

Model.attribute_was return previous value :D

For rails 5.1+

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

Something like:

before_save object
do_something_with object.name_before_last_save
end

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 source from docs

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

_before_last_save source from docs

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

You can see a better example here