系列文章汇总《Ruby on Rails 2.1新特性》

新的rails中activerecord拥有了检查record object是否有改变的能力,即dirty object.
这个功能非常简单灵活:

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

# Track changes to individual attributes with
# attr_name_changed? accessor
article.title  #=> "Title"
article.title = "New Title"
article.title_changed? #=> true

# Access previous value with attr_name_was accessor
article.title_was  #=> "Title"

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

你还可以直接查询对象所有改变了的属性,(继续上例):

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

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

注意: 如果你保存了一个dirty object,他就会清除所有改变的痕迹:

article.changed?  #=> true
article.save  #=> true
article.changed?  #=> false

如果你要使用attr=以外的方法改变对象属性的时候,可以使用attr_name_will_change!来告诉对象注意属性的变化:

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

原文：http://ryandaigle.com/
来自：http://www.javaeye.com/news/2349

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