20141208102001_add_supplier_id_to_gifts.rb

class Datafixes::AddSupplierIdToGifts < Datafix
  def self.up
    execute(<<-SQL)
    UPDATE gifts SET supplier_id = products.selected_supplier
    FROM (SELECT gifts.id as gift_id, products.supplier_id as selected_supplier FROM gifts JOIN products
      ON gifts.selected_product_id = products.id
      WHERE stage = 'redeemed') as products
    WHERE gifts.id = products.gift_id
    SQL
  end
end

20141208102001_add_supplier_id_to_gifts_spec.rb

require "rails_helper"
require Rails.root.join("db", "datafixes", "20141208102001_add_supplier_id_to_gifts")

describe Datafixes::AddSupplierIdToGifts do
  describe ".up" do
    let!(:gift1) do
      gift = FactoryGirl.build(:redeemed_gift, supplier: nil)
      gift.save(validate: false)
      gift
    end

    let!(:gift2) do
      gift = FactoryGirl.build(:redeemed_gift, selected_product: gift1.selected_product, supplier: nil)
      gift.save(validate: false)
      gift
    end

    let!(:gift3) do
      gift = FactoryGirl.build(:redeemed_gift, supplier: nil)
      gift.save(validate: false)
      gift
    end

    let!(:excluded_gift1) { FactoryGirl.create(:sent_gift) }
    let!(:excluded_gift2) { FactoryGirl.create(:gift) }

    it "should populate the supplier" do
      Datafixes::AddSupplierIdToGifts.up
      expect(gift1.reload.supplier).to eq gift1.selected_product.supplier
      expect(gift2.reload.supplier).to eq gift1.selected_product.supplier
      expect(gift2.reload.supplier).to eq gift2.selected_product.supplier
      expect(gift3.reload.supplier).to eq gift3.selected_product.supplier

      expect(excluded_gift1.reload.supplier).to be_nil
      expect(excluded_gift2.reload.supplier).to be_nil
    end
  end
end