code: def get_lookup_value(self, value):
          
          choices = self._field_choices()
          if choices:
              if isinstance(value, list):
                  return [c[0] for c in choices if c[1] in value]
              else:
                  for c in choices:
                      if c[1] == value:
                          return c[0]
          return value
docs: Override this method to convert displayed values to lookup values