patch.rb

require 'active_record/autosave_association'

module ActiveRecord
  module AutosaveAssociation

    private
    
    def save_belongs_to_association(reflection)
      association = association_instance_get(reflection.name)
      return unless association && association.loaded? && !association.stale_target?

      record = association.load_target
      if record && !record.destroyed?
        autosave = reflection.options[:autosave]

        if autosave && record.marked_for_destruction?
          foreign_key = Array(reflection.foreign_key)
          foreign_key.each { |key| self[key] = nil }
          record.destroy
        elsif autosave != false
          saved = record.save(validate: !autosave) if record.new_record? || (autosave && record.changed_for_autosave?)

          if association.updated?
            primary_key = Array(compute_primary_key(reflection, record)).map(&:to_s)
            foreign_key = Array(reflection.foreign_key)

            primary_key_foreign_key_pairs = primary_key.zip(foreign_key)
            primary_key_foreign_key_pairs.each do |primary_key, foreign_key|
              association_id = record._read_attribute(primary_key)
              self[foreign_key] = association_id unless self[foreign_key] == association_id
            end
            association.loaded!
          end

          saved# if autosave
        end
      end
    end
    
  end
end