Imagine you have a <code>Post</code> class, which can have many <code>Comment</code> objects. You want the associated <code>Comment</code>s to be ordered by the date they were posted on. 

To do this, add a <code>posted_on</code> field, then define your [[Associations]] like this:

<pre>
<code>
class Post< ActiveRecord::Base
  has_many :comments, :order => "posted_on"
  ...
end
</code>
</pre>

For more information see the ActiveRecord documentation for "associations documentation":http://api.rubyonrails.com/classes/ActiveRecord/Associations/ClassMethods.html