module BulkUpdatable
  def bulk_update(objects, attribute)
    return unless objects.any?

    query = build_query_for(objects, attribute)
    connection.execute(query)
  end

private

  def build_query_for(objects, attribute)
    values = objects.map { |object| sanitized_values(object, attribute) }

    <<-SQL
      UPDATE #{table_name}
      SET #{attribute} = tmp_table.#{attribute}
      FROM (VALUES #{values.join(',')}) AS tmp_table(id, #{attribute})
      WHERE #{table_name}.id = tmp_table.id
    SQL
  end

  def sanitized_values(object, attribute)
    sanitize_sql_array(['(?, ?)', object.id, object.read_attribute(attribute)])
  end

end