How to edit multiple attached images using ActiveStorage `has_many_attached` in ActiveAdmin - ruby-on-rails

Question

I have a simple model that can have multiple images attached via ActiveStorage handling the file storage.
I am using ActiveAdmin to edit my model and to upload/attach the images - so far no problems.
The problem is, when I want to edit my model, and add new images, then the previous ones are deleted, and only the new ones added.
I can do a preview of already attached images, and could also delete them separately, but how do I achieve, that by uploading new images, the old ones are NOT deleted?
My model:
class Post < ActiveRecord::Base
has_many_attached :images
end
My ActiveAdmin page:
ActiveAdmin.register AdminPost do
permit_params images:[]
form do |f|
f.input :images, as: :file, input_html: { multiple: true }
if #resource.images.exists?
#resource.images.map do |m|
para image_tag m
end
end
end
end

Answer 1

Assuming you are using rails 6.0+;
you can solve this by adding following code in to your environments (i.e - development.rb )
https://github.com/rails/rails/issues/35817#issuecomment-628654948
config.active_storage.replace_on_assign_to_many = false
in your form,
form do |f|
f.input :images, as: :file, input_html: { multiple: true }
f.object.images.each do |image|
span image_tag(image)
end
end

Answer 2

So I chose the way of adding the new attachments manually, so they don't replace the existing attached images.
I added a field to handle the posted images, and a method to add them in my model.
class Post < ActiveRecord::Base
has_many_attached :images
attr_accessor :new_images
def attach_images
return if new_images.blank?
images.attach(new_images)
self.new_images = []
end
end
And the ActiveAdmin page controller handles the upload, and calls the new method:
ActiveAdmin.register AdminPost do
permit_params new_images:[]
form do |f|
f.input :new_images, as: :file, input_html: { multiple: true }
if #resource.images.exists?
#resource.images.map do |m|
para image_tag m
end
end
end
controller do
after_save :add_images
def add_images(post)
post.attach_images
end
end
end