I’m also wondering about this. I’m thinking it would be useful if one could define the allowed params and their expected format either in a file that is dynamically included in the controller based on the type of the delegatee, or as a method in the delegatee’s model. But I’m not sure of the best way to combine that with params.expect for the parent class, which is needed for accept_nested_attributes_for to work its magic… Perhaps producing a separate parameters hash for the type and merging that with the parent’s params hash is the way forward.