docs: def _validate_unique(self, create=True):
          """ Validate the unique constraints for the entity """
          # Build the filters from the unique constraints
          filters, excludes = {}, {}
  
          for field_name, field_obj in self.meta_.unique_fields:
              lookup_value = getattr(self, field_name, None)
              # Ignore empty lookup values
              if lookup_value in Field.empty_values:
                  continue
              # Ignore identifiers on updates
              if not create and field_obj.identifier:
                  excludes[field_name] = lookup_value
                  continue
              filters[field_name] = lookup_value
  
          # Lookup the objects by the filters and raise error on results
          for filter_key, lookup_value in filters.items():
              if self.exists(excludes, **{filter_key: lookup_value}):
                  field_obj = self.meta_.declared_fields[filter_key]
                  field_obj.fail('unique',
                                 entity_name=self.__class__.__name__,
                                 field_name=filter_key)