was_changed

Based on ActiveRecord Dirty Objects, was_changed extends changed? et al to persist past the object save. As it's based on Dirty, I'll borrow the example from the announcement of Dirty.

Example

article = Article.find(:first)
article.save
article.was_changed?  #=> false

# Track changes to individual attributes with
# attr_name_was_changed? accessor
article.title  #=> "Title"
article.title = "New Title"
article.title_changed? #=> true
article.save
article.title_was_changed? #=> true
article.title_changed? #=> false

# Access previous value with attr_name_before_save_was accessor
article.title_before_save_was  #=> "Title"

# See both previous and current value with attr_name_before_save_change accessor
article.title_before_save_change  #=> ["Title", "New Title"]

# Get a list of changed attributes
article.was_saved  #=> ['title']

# Get the hash of changed attributes and their previous and current values
article.saved_changes  #=> { 'title' => ["Title", "New Title"] }

It uses Dirty's framework, so will_change! will also work:

article = Article.find(:first)
article.title_will_change!
article.title.upcase!
article.save
article.title_before_save_change  #=> ['Title', 'TITLE'] 

Copyright (c) 2008 Multiplay (UK) Ltd., released under the MIT license