You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: post_replacement.rb
    path of file: ./repos/danbooru/app/models
    
    the code of the file until where you have to start completion: # frozen_string_literal: true

class PostReplacement < ApplicationRecord
  belongs_to :post
  belo
    
  def initialize_fields
    self.original_url = post.source
    self.old_file_ext = post.file_ext
    self.old_file_size = post.file_size
    self.old_image_width = post.image_width
    self.old_image_height = post.image_height
    self.old_md5 = post.md5
    self.old_media_asset = post.media_asset
  end