save_collection_association

# File activerecord/lib/active_record/autosave_association.rb, line 388
      def save_collection_association(reflection)
        if association = association_instance_get(reflection.name)
          autosave = reflection.options[:autosave]

          # By saving the instance variable in a local variable,
          # we make the whole callback re-entrant.
          new_record_before_save = @new_record_before_save

          # reconstruct the scope now that we know the owner's id
          association.reset_scope

          if records = associated_records_to_validate_or_save(association, new_record_before_save, autosave)
            if autosave
              records_to_destroy = records.select(&:marked_for_destruction?)
              records_to_destroy.each { |record| association.destroy(record) }
              records -= records_to_destroy
            end

            records.each do |record|
              next if record.destroyed?

              saved = true

              if autosave != false && (new_record_before_save || record.new_record?)
                association.set_inverse_instance(record)

                if autosave
                  saved = association.insert_record(record, false)
                elsif !reflection.nested?
                  association_saved = association.insert_record(record)

                  if reflection.validate?
                    errors.add(reflection.name) unless association_saved
                    saved = association_saved
                  end
                end
              elsif autosave
                saved = record.save(validate: false)
              end

              raise(RecordInvalid.new(association.owner)) unless saved
            end
          end
        end
      end