attachment_cache is not working with nested attributes

[mdesantis]

I'm facing this issue on Rails 5.1.2 and Carrierwave 1.1.0, even using rails console:

irb(main):013:0> ci = Cover::Item.find 18
irb(main):014:0> new_attributes = {"id"=>"69", "attachment_cache"=>"1500657554-16427-0005-2355/KITTY.jpg"}
irb(main):015:0> ci.update teaser_image_horizontal_attributes: new_attributes
=> true

But the image file is not updated,
but if I do:

ci.teaser_image_horizontal.update attachment_cache: "1500657554-16427-0005-2355/KITTY.jpg"

it gets updated

[mdesantis]

I found that after_validation callback is reached in both cases, but before_save is reached in not nested attributes case only

[mdesantis]

It seems that if you pass some other attribute to be updated, like for example updated_at: Time.now, works

[mdesantis]

Workaround:

  # inside the model class with `mount_uploader`
  before_validation do
    attachment_will_change! if attachment_cache.present?
  end