public function addRoleByName($role_name)
    {
        $role = static::$app['db']->connection()
            ->table('roles')->where('name', '=', $role_name)->first();

        if (! $role)
            throw new \RuntimeException('No role with that name found.');

        if (is_array($role))
            return $this->addRoleById($role['id']);
        elseif (is_object($role))
            return $this->addRoleById($role->id);
        else
            throw new \UnexpectedValueException('Value returned not array or instance of BridgeRole.');
    }