silverstripe/sapphire — pull request #754 by howardgrigg (2012-08-30 05:16:15+00:00)
Title: API 

Before you could not modify the extraFields on a many_many relation without deleting and recreating the relation. This meant you would lose all saved extraFields and just have the one you added.

This is fixed with a new function modify().

Let me know what you think.