Attachments should be detached when assigned a blank value

[kylefox]

ActiveStorage allows attachments to be attached by assigning a string representing a blob's signed_id. This works brilliantly because it enables the same params conventions used when assigning other attributes through forms → controllers → models:

params = { user: { image: 'eyJfcmF--e31aef3' } }

However, it's surprising that setting the attachment to an empty string does not detach the attachment:

params = { user: { image: '' } } # => InvalidSignature

It feels more Railsy to treat the empty string as a special case that detaches the attachment.

This would allow attachments to be removed in a way that mirrors how they are added (i.e. posting hidden field values) instead of having to call @user.image.detach in a controller.

For example, this would handle both attaching and detaching @user.image:

@user.update_attributes(params.require(:user).permit(:name, :email, :image))

Steps to reproduce

1. Assign an attachable to the attachment: @user.image = blob.signed_id
2. Assign an empty string to the attachment: @user.image = ''

Expected behavior

• The attachment is detached, i.e. @user.image.detach.

Actual behavior

• ActiveSupport::MessageVerifier::InvalidSignature is raised.

System configuration

• Rails version: Rails 5.2.0
• Ruby version: ruby 2.5.1p57 (2018-03-29 revision 63029) [x86_64-darwin17]

[kaspth]

Thanks for the request! We don't keep these on the issue tracker, but on the Rails Core mailing list. If you're interested in trying a PR, here's the line:

rails/activestorage/lib/active_storage/attached/model.rb

Line 41 in 05bef14

if attachable.nil?

It seems has_many_attached already supports being passed nil or an empty array and then clearing out all the attachments.

I can't guarantee we'll accept it even once we see the code, but please do investigate :)

[kylefox]

Thanks @kaspth! I submitted it here because it feels more like a bug than feature request — especially if has_many_attached behaves this way. But I'll send it over to the mailing list. 👍

[kylefox]

Here's the mailing list link if anyone is interested in continuing the discussion:

• Attachments should be detached when assigned a blank value