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: 20140425135354_add_topic_custom_fields.rb
    path of file: ./repos/discourse/db/migrate
    
    the code of the file until where you have to start completion: # frozen_string_literal: true

class AddTopicCustomFields < ActiveRecord::Migration[4.2]
  def change
    create_table :topic_custom_fields do |t|
      t.integer :topic_id, null: false
      t.string :name, limit: 256, null: false
      t.text :value
      t.timestamps null: false
    end

    add_index :topic_custom_fields, %i[topic_id name]

    # migrate meta_data into custom fields
    execute <<-SQL
      INSERT INTO topic_custom_fields(
    
  def change
    create_table :topic_custom_fields do |t|
      t.integer :topic_id, null: false
      t.string :name, limit: 256, null: false
      t.text :value
      t.timestamps null: false
    end

    add_index :topic_custom_fields, %i[topic_id name]

    # migrate meta_data into custom fields
    execute <<-SQL
      INSERT INTO topic_custom_fields(topic_id, name, value)
        SELECT id, (each(meta_data)).key, (each(meta_data)).value
            FROM topics WHERE meta_data <> ''
    SQL

    remove_column :topics, :meta_data
  end