The goal here is to improve ActiveModel support so that Draper can
work seamlessly with Rails' FormHelpers, proxying the model's #errors
method.
I also added support for ActiveModel::Errors, adding a proxy to the
model's #errors method only if it's a descendant of
ActiveModel::Validations.
Also some refactoring was done. Draper now proxies #to_param and #id
methods only if the model is an ActiveModel descendant.
Other things I did include:
- created Draper::ActiveModelSupport::Proxies, which contains the
methods for proxying default methods(to_param, id, etc) depending
on the ancestors
- wrote specs for class with ActiveModel as ancestor
- wrote specs for class without ActiveModel as ancestor
