Laravel check if vaue exists

I am new in coding and was hoping you guys can help.

I am trying out Laravel 5 on a new project and I need some assistance with a few things.

Here is my problem .

1. I am trying to check a sponsor_id (sponsor email) on user registration if it exists when a new user register in the system and if it does exists then set (entry_by==user_id).

Here is my newbie code :

if ($referrer == $email)
        {
            $entry_by == $id;
        }
            else
            {
                $message= " There is an error on the referrer code provided.";
            }

Thanks

via Chebli Mohamed