Deleting Paperclip Attachments with ActiveAdmin

Deleting Paperclip Attachments with ActiveAdmin

This technique will be consistent with how Rails' built-in nested attributes for associations work once the magic and mystery is removed.

To delete an attachment. an Author model with an avatar attachment:

class Author < ApplicationRecord
  ...
  has_attached_file :avatar
  ...
end

Step 1: Add <attachment_name>_attributes= writer method

As accepts_nested_attributes_for only works with ActiveRecord associations like has_one, has_many, etc. we will not make direct use of it, but manually add the writer method it generates itself.

(To understand how nested attributes work in Rails see http://api.rubyonrails.org/classes/ActiveRecord/NestedAttributes/ClassMethods.html).

Add a <attachment_name>_attributes= writer method like below to your model that already uses has_attached_file:

class Author < ApplicationRecord
  ...
  has_attached_file :avatar

+ def avatar_attributes=(attributes)
+   # Marks the attachment for destruction on next save,
#   # if the attributes hash contains a _destroy flag:
+   avatar.clear if has_destroy_flag?(attributes)
+ end
end

The method calls Paperclip::Attachment#clear to mark the attachment for destruction when the model is next saved.

Step 2: Setup ActiveAdmin form and strong params

Open app/admin/authors.rb (use the correct file path for your app) and setup strong parameters to permit the _destroy flag nested attribute:

# File: app/admin/authors.rb
ActiveAdmin.register Author do

-  permit_params :name, :bio, :avatar
+  permit_params :name, :bio, :avatar, avatar_attributes: [:_destroy]