require 'active_record'

module ActiveRecordMysqlIndexHint
  def use_index(*args)
    from_with_index_hint 'USE', *args
  end

  def force_index(*args)
    from_with_index_hint 'FORCE', *args
  end

  def ignore_index(*args)
    from_with_index_hint 'IGNORE', *args
  end

  private
  def from_with_index_hint(hint_type, *args)
    return self if args.blank?
    indexes = args.map {|index| connection.quote_column_name index }
    self.from([Arel.sql("#{quoted_table_name} #{hint_type} INDEX(#{indexes.join(', ')})")])
  end
end

ActiveSupport.on_load :active_record do
  require 'active_record/relation/query_methods'
  ActiveRecord::Base.extend ActiveRecordMysqlIndexHint
  ActiveRecord::Relation.send :include, ActiveRecordMysqlIndexHint
end