foodsoft/db/migrate/021_remove_table_article_prices.rb

class RemoveTableArticlePrices < ActiveRecord::Migration[4.2]
  def self.up
    puts 'create columns in articles ...'
    add_column 'articles', 'clear_price', :decimal, precision: 8, scale: 2, default: 0.0, null: false
    add_column 'articles', 'gross_price', :decimal, precision: 8, scale: 2, default: 0.0, null: false
    add_column 'articles', 'tax', :float
    add_column 'articles', 'refund', :decimal, precision: 8, scale: 2, default: 0.0, null: false
    add_column 'articles', 'unit_quantity', :integer, default: 1,   null: false
    add_column 'articles', 'order_number', :string
    add_column 'articles', 'created_at', :datetime
    add_column 'articles', 'updated_at', :datetime

    # stop auto-updating the timestamps to make the data-copy safe!
    Article.record_timestamps = false

    puts 'now copy values of article_prices into new articles-columns...'
    Article.find(:all).each do |article|
      price = article.current_price
      article.update!(clear_price: price.clear_price,
                      gross_price: price.gross_price,
                      tax: price.tax,
                      refund: price.refund,
                      unit_quantity: price.unit_quantity,
                      order_number: price.order_number,
                      updated_at: price.updated_on,
                      created_at: price.updated_on)
    end

    puts 'delete article_prices, current_price attribute'
    drop_table :article_prices
    remove_column :articles, :current_price_id
  end

  def self.down
    add_column :articles, :current_price_id, :integer
    create_table 'article_prices', force: true do |t|
      t.integer  'article_id', default: 0,   null: false
      t.decimal  'clear_price',   precision: 8, scale: 2, default: 0.0, null: false
      t.decimal  'gross_price',   precision: 8, scale: 2, default: 0.0, null: false
      t.float    'tax', default: 0.0, null: false
      t.decimal  'refund', precision: 8, scale: 2, default: 0.0, null: false
      t.datetime 'updated_on'
      t.integer  'unit_quantity', default: 1, null: false
      t.string   'order_number'
    end

    # copy data from article now into old ArticlePrice-object
    Article.find(:all).each do |article|
      price = ArticlePrice.create(clear_price: article.clear_price,
                                  gross_price: article.gross_price,
                                  tax: article.tax,
                                  refund: article.refund,
                                  unit_quantity: article.unit_quantity,
                                  order_number: article.order_number.presence,
                                  updated_on: article.updated_at)

      article.update_attribute(:current_price, price)
      price.update_attribute(:article, article)
    end

    # remove new columns
    remove_column 'articles', 'clear_price'
    remove_column 'articles', 'gross_price'
    remove_column 'articles', 'tax'
    remove_column 'articles', 'refund'
    remove_column 'articles', 'unit_quantity'
    remove_column 'articles', 'order_number'
    remove_column 'articles', 'created_at'
    remove_column 'articles', 'updated_at'
  end
end