```ruby
module Adminpanel
  class Image < ActiveRecord::Base
    include Adminpanel::Base

    belongs_to :model, polymorphic: true

    before_save :store_file_size_and_content_type
    after_save :delete_old_unused_images
    before_destroy :remove_attachment
  
    private
      def remove_attachment
        self.remove_file!
      end
    
      def store_file_size_and_content_type
        if file.present? && file_changed?
          self.content_type = file.file.content_type
          self.file_size = file.file.size
        end
      end

      def delete_old_unused_images
        self.class.where('"adminpanel_images"."created_at" < (?)', Time.now - 30.minutes).delete_all(
          model_id: nil,
          model_type: nil,
          type: self.type,
        )
      end
  end
end
```

Update callback syntax for compatibility
user
```ruby
module Adminpanel
  class Image < ActiveRecord::Base
    include Adminpanel::Base

    belongs_to :model, polymorphic: true

    before_save :store_file_size_and_content_type
    after_save :delete_old_unused_images
    before_destroy :remove_attachment

    private
      def remove_attachment
        self.remove_file!
      end

      def store_file_size_and_content_type
        if file.present? && file_changed?
          self.content_type = file.file.content_type
          self.file_size = file.file.size
        end
      end

      def delete_old_unused_images
        self.class.where({ created_at: (Time.now - 30.minutes)..Time.now})
                  .delete_all(
                    model_id: nil,
                    model_type: nil,
                    type: self.type,
                  )
      end
  end
end
```
assistant