# File lib/dm-aggregates/query.rb, line 13
      def assert_valid_fields_with_operator(fields, unique)
        operators, fields = fields.partition { |f| f.kind_of?(DataMapper::Query::Operator) }

        operators.each do |operator|
          target = operator.target

          unless target == :all || target.kind_of?(Property) && target.model == model && @properties.include?(target)
            raise ArgumentError, "+options[:fields]+ entry #{target.inspect} does not map to a property in #{model}"
          end
        end

        assert_valid_fields_without_operator(fields, unique)
      end