This is probably a silly question but so far but, it seems like I can only use integer fields for the index attribute of a list. How can I use a list with the ordering by a created_date... I would think it would be something like the following (which doesn't work):

<list name="MyList">
<key column="some_id" />
<index column="created_date"/>
<one-to-many class="SomeClass" />
</list>

When I try to use this type of situation, I receive an error stating:
"Bad format for number..."

So, I understand that you can only have numbers in the index field, but how could I have a list that was ordered by a date? Thanks for any help.

use <bag order-by>