jnunemaker/mongomapper — pull request #414 by md5 (2012-05-07 22:58:12+00:00)
Title: Declare type key on polymorphic belongs_to

When a belongs_to association is marked as :polymorphic => true, add a model key of type String for the "type_key_name" field in addition to the key of type ObjectId for "foreign_key"