protected function assignPrimaryKey(array & $mappers)
    {
        $foundPrimary = false;

        foreach ($mappers as $mapper) {
            if ($foundPrimary) {
                $mapper->field->isPrimary = false;
                $mapper->field->isAutoIncrement = false;
                continue;
            }

            if ($mapper->field->isPrimary()) {
                $mapper->field->isPrimary = true;
                $foundPrimary = true;
            }
        }

        return $this;
    }