"Gregg Pollack of RailsEnvy, co-author of the infamous Rails vs PHP/Java "commercials", has put together a presentation cum screencast about ActiveRecord and object mapping in general. It's based on a presentation given on June 16 to the Orlando Ruby User Group. He covers the origins of ActiveRecord, the rationale for its use, and walks through topics like many to many relationships, polymorphic relationships, and tagging."