Append files in Active storage without removing existing

Solution 1 - introduce setter method on model that appends

# a/m/entry.rb
class Entry < ApplicationRecord
  has_many_attached :files

  def append_files=(attachables)
    files.attach(attachables)
  end
end

new files get appended

# a/c/entries_controller.rb
def entry_params
  params.require(:entry).permit(append_files: [])
end

new files replaced existing files

# a/c/entries_controller.rb
def entry_params
  params.require(:entry).permit(files: [])
end

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Solution 2 - Globally enable new files should append

# config/application.rb
config.active_storage.replace_on_assign_to_many = false

new files get appended

# a/c/entries_controller.rb
def entry_params
  params.require(:entry).permit(files: [])
end