问题
When using autocomplete in the console, I often see "_was" postpended to my attributes. But I can't find any documentation or best practices for usage. What does it do and how should it be used?
Example: user.fname has the method user.fname_was
Using source_location, I've tracked it down to: active_model/attribute_methods.rb", line 296 but there isn't anything specific.
回答1:
That is a part of ActiveModel::Dirty You can see it here https://github.com/rails/rails/blob/af64ac4e5ce8406137d5520fa88e8f652ab703e9/activemodel/lib/active_model/dirty.rb#L146 Example
person = Person.find_by_name('Uncle Bob')
person.changed? # => false
Change the name:
person.name = 'Bob'
person.changed? # => true
person.name_changed? # => true
#method _was return prev attribute value
person.name_was # => 'Uncle Bob'
person.name_change # => ['Uncle Bob', 'Bob']
person.name = 'Bill'
person.name_change # => ['Uncle Bob', 'Bill']
来源：https://stackoverflow.com/questions/13906635/what-is-the-activemodel-method-attribute-was-used-for