Generic relations’ fields are be frozen, but unfortunately not the GenericForeignKey itself (see ORM Freezing for a reason why). To add it back onto a model, add the import for generic at the top of the migration and then in the body of forwards() put:
gfk = generic.GenericForeignKey() gfk.contribute_to_class(orm.FooModel, "object_link")
This will add the GenericForeignKey onto the model as model.object_link. You can pass the optional content_type and id field names into the constructor as usual.
Also, be careful when using ContentType; make sure to use the frozen orm[‘contenttypes.ContentType’], and don’t import it directly, otherwise comparisons may fail.