replace

# File activerecord/lib/active_record/associations/collection_association.rb, line 294
      def replace(other_array)
        other_array.each { |val| raise_on_type_mismatch(val) }
        original_target = load_target.dup

        transaction do
          delete(target - other_array)

          unless concat(other_array - target)
            @target = original_target
            raise RecordNotSaved, "Failed to replace #{reflection.name} because one or more of the "                                    "new records could not be saved."
          end
        end
      end