def reposition_parts!
      reload.parts.each_with_index do |part, index|
        part.update_columns position: index
      end
    end
def reposition_parts!
      reload.parts.each_with_index do |part, index|
        part.update_columns position: index
      end
    end
Repositions the child page_parts that belong to this page.
 This ensures that they are in the correct 0,1,2,3,4... etc order.