Migrate url to template_data hstore

add_template_data_to_contents.rb

class AddTemplateDataToContents < ActiveRecord::Migration[5.0]
  def up
    add_column :contents, :template_data, :hstore, default: '', null: false
    execute <<~END
      UPDATE contents
      SET template_data = hstore('url', subquery.url)
      FROM (SELECT id, url FROM contents) as subquery
      WHERE contents.id=subquery.id;
    END
    remove_column :contents, :url, :string
  end

  def down
    add_column :contents, :url, :string
    execute <<~END
      UPDATE contents
      SET url = subquery.turl FROM (SELECT id, template_data->'url' as turl FROM contents) as subquery
      WHERE contents.id=subquery.id;
    END
    remove_column :contents, :template_data
  end
end