Export MongoDB collection to ActiveRecord Model directly. Used for MongoId to ActiveRecord migration.

database_transformer.rb

# frozen_string_literal: true

require 'colorize'

module DatabaseTransformer
  attr_reader :database

  def initialize(database)
    @database = database
  end

  def import(collection_name, *obsolete_columns, **rename_columns)
    collection = Mongoid::Clients.default.collections.select do |c|
      c.namespace == "#{database}.#{collection_name.to_s.pluralize}"
    end.first

    unless collection.present?
      STDOUT.puts "#{collection_name.to_s.yellow}: skipped"
      STDOUT.puts
      return
    end

    constant = collection_name.to_s.singularize.camelcase.constantize
    reset_callbacks constant

    DatabaseTransformer.profiling do
      collection_count = collection.find.count
      collection.find.each_with_index do |document, index|
        delete_obsolete_columns document, obsolete_columns
        update_rename_columns document, rename_columns
        update_id_columns document
        document = yield document if block_given?

        insert_record constant, document
        STDOUT.puts "#{index}/#{collection_count}\n" if (index % 1000).zero?
      end
    end
  end
  
  private
  
  def reset_callbacks(constant)
    %i(create save update).each do |callback|
      constant.reset_callbacks callback
    end
  end

  def delete_obsolete_columns(document, obsolete_columns)
    obsolete_columns.each { |column| document.delete column.to_s }
  end

  def update_rename_columns(document, rename_columns)
    document.deep_transform_keys do |key|
      new_key = rename_columns[key.to_sym]
      new_key.present? ? new_key : key
    end
  end

  def update_id_columns(document)
    document.map! do |key, value|
      next ['uuid', value.to_s] if key == '_id' # save _id to uuid temp
      if key.end_with? '_id' # save xx_id to xx_uuid
        uuid_key = key[0...-2] + 'uuid'
        [uuid_key, value.to_s]
      else
        [key, value] # normal case
      end
    end
    Hash[document]
  end

  def insert_record(constant, params)
    model = constant.new params
    model.save! validate: false
  rescue Exception => exception
    STDERR.puts "Import Error: #{exception}"
    raise exception
  end

  def self.profiling
    started_at = Time.now

    yield if block_given?

    seconds = Time.now.to_i - started_at.to_i
    STDOUT.puts "Completed: #{seconds.to_s.green} seconds\n"
    STDOUT.puts "\n"
  end
end

transformer = DatabaseTransformer.new 'draven_production'
transformer.import :post, :_slugs, :status, title: :name, desc: :description, _type: :type
# Restore relation with https://gist.github.com/Draveness/c0798fb1272f483a176fa67741a3f1ee