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: 115_drops_categories_for_tags.publify_core_engine.rb
    path of file: ./repos/publify/db/migrate
    
    the code of the file until where you have to start completion: # frozen_string_literal: true

class DropsCategoriesForTags < ActiveRecord::Migration[4.2]
  class Categorization < ActiveRecord::Base
    belongs_to :article
    belongs_to :category
  end

  class Category < ActiveRecord::Base
    has_many :categorizations
    has_many :articles, through: :categorizations
  end

  def up
    # First, we migrate categories into tags
    Category.find_each do |cat|
      # Does a tag with the same permalink exist?
      tag = Tag.find_
    
  def up
    # First, we migrate categories into tags
    Category.find_each do |cat|
      # Does a tag with the same permalink exist?
      tag = Tag.find_or_create_by(name: cat.permalink) do |tg|
        tg.display_name = cat.name
      end

      Redirect.create(from_path: "category/#{cat.permalink}",
                      to_path: File.join(Blog.first.base_url, "tag", tag.name))
      cat.articles.each do |article|
        article.tags << tag
        article.save
      end
    end

    drop_table :categorizations
    drop_table :categories
  end