docs: def value(self):
          """convenience method to just get one value or tuple of values for the query"""
          field_vals = None
          field_names = self.fields_select.names()
          fcount = len(field_names)
          if fcount:
              d = self._query('get_one')
              if d:
                  field_vals = [d.get(fn, None) for fn in field_names]
                  if fcount == 1:
                      field_vals = field_vals[0]
  
          else:
              raise ValueError("no select fields were set, so cannot return value")
  
          return field_vals