Is this a good Ruby copy-constructor?

I had the need to copy a model instance in a Rails application I'm writing. I am not a Ruby wizz yet, so I am just going to ask. Is this a good copy-constructor in Ruby/Rails terms?

  def copy_constructor
   course = Course.new(self.attributes)
   course.id = nil # make copy transient

   # the "trainers" n-m relation is not copied in "new", as it is not an attribute on the model
   course.trainers = self.trainers
   course.trainer_ids = self.trainer_ids

   return course
 end

The model I am copying is "Course" and it has a N-M relation to a "Trainer" model. I use the "self.attributes" call, to set attributes on the new instance, but the relations are not copied. Also, I set "id" to nil, to make ActiveRecord think it is transient, which makes ".save" do an insert.

Any better way to do this?