docs: def delete(self):
          """ Deletes one instance """
          if self.instance is None:
              raise CQLEngineException("DML Query instance attribute is None")
  
          ds = DeleteStatement(self.column_family_name, timestamp=self._timestamp)
          for name, col in self.model._primary_keys.items():
              if (not col.partition_key) and (getattr(self.instance, name) is None): continue
              ds.add_where_clause(WhereClause(
                  col.db_field_name,
                  EqualsOperator(),
                  col.to_database(getattr(self.instance, name))
              ))
          self._execute(ds)