private function FieldCondition($field, $value)
        {
            $tbl = $this->Table();
            $mapper = $this->FieldMapper($field);
            $dbVal = $mapper->ToDBString($value);
            
            $sql = $this->SqlBuilder();
            
            if ($dbVal === null)
                return $sql->IsNull($tbl->Field($field));
            else
                return $sql->Equals($tbl->Field($field), $sql->Value($dbVal));
        }