def select(fields)
      if (fields == []) || (fields.nil?)
        fields = [:_id]
      end
      clone.tap {|q| q.options[:fields] = fields}
    end
def select(fields)
      if (fields == []) || (fields.nil?)
        fields = [:_id]
      end
      clone.tap {|q| q.options[:fields] = fields}
    end
Add select method to select the fields to return