# File lib/arel/table.rb, line 32
    def primary_key
      if $VERBOSE
        warn "primary_key (\#{caller.first}) is deprecated and will be removed in ARel 3.0.0\n"
      end
      @primary_key ||= begin
        primary_key_name = @engine.connection.primary_key(name)
        # some tables might be without primary key
        primary_key_name && self[primary_key_name]
      end
    end