Polymorphic Paperclip class with unique partial ActiveRecord index on :default_image

create_image_attachment.rb

# db/migrations/xxxxxxxxxxxxxx_create_image_attachment.rb
class CreateImageAttachments < ActiveRecord::Migration[5.0]
  def change
    create_table :image_attachments do |t|
      t.belongs_to :imageable, polymorphic: true
      t.attachment :data
      t.boolean    :default, default: false

      t.timestamps
    end

    add_index :image_attachments, [:imageable_id, :imageable_type, :default], unique: true, where: '"default" = TRUE', name: :unique_on_imageable_default
  end
end

image_attachment.rb

# app/models/image_attachment.rb
class ImageAttachment < ApplicationRecord
  belongs_to :imageable, polymorphic: true

  has_attached_file :data,
    styles:          { thumb:  '120x120#',            medium: '600x600>'           },
    convert_options: { thumb:  '-quality 75 -strip',  medium: '-quality 90 -strip' }

  validates_attachment_presence     :data
  validates_attachment_size         :data, less_than:    PAPERCLIP_IMAGE_SIZE_LIMIT
  validates_attachment_content_type :data, content_type: PAPERCLIP_IMAGE_CONTENT_TYPE

  validates :default, uniqueness: { scope: :imageable }, if: :default? 
  
  def undefault!
    update(default: false)
  end

  def default!
    imageable.default_image.undefault! if imageable.default_image
    update(default: true)
  end
end

imageable.rb

# app/models/concerns/imageable.rb
module Imageable
  extend ActiveSupport::Concern

  included do
    has_many :image_attachments, as: :imageable, dependent: :destroy
    alias_attribute :images, :image_attachments
  end

  def default_image
    images.find_by(default: true)
  end
end

I dont understand how it works, I tried to implement this code but its not saving the attached file, i dont understand why :/