code: def property2field(self, prop, instance=True, field_class=None, **kwargs):
          
          field = super().property2field(prop, instance, field_class, **kwargs)
          # when a column is not nullable, mark the field as required
          if hasattr(prop, 'columns'):
              col = prop.columns[0]
              if not col.primary_key and not col.nullable:
                  field.required = True
          return field
docs: Overridden to mark non-nullable model columns as required (unless it's the
          primary key, because there's no way to tell if we're generating fields
          for a create or an update).